Partly cleanup and simplify cmake/configs/posix_sitl_* config files.

While the config_sitl_rcS_dir is used more extensively (and actually
only depending on the base cmake target), the variables
config_sitl_viewer and config_sitl_debugger are just used to be
passed on for the run_config target; config_sitl_debugger is even
*always* 'disable'. Hence, they don't really need to be cached
(INTERNAL or not). Before this patch FILEPATH was used instead
of INTERNAL, but I doubt very much that that was intended. That
only makes sense when cmake-gui would be used and then would pop-up
a file browser to let the user pick a file (while really they
need to pick a directory, so it's wrong either way).

The ONLY reason caching would be used is when a developer edits
the build_posix_sitl_*/CMakeCache.txt files, changes these values
and then runs cmake in the build directory again, now overriding
the values intended here. Nevertheless, I left in the caching.

The main change in this commit (that theoretically has no real effect)
is that I removed the duplicated maintenance of
posix_sitl_broadcast.cmake. When that file was added, it was an
exact copy of posix_sitl_default.cmake and is since not always
maintained to remain the same. I don't think that difference is
in anyway relevant for the broadcasting part though.

Note that I think that something like that also holds for the
posix_sitl_replay.cmake; it would be a lot better - maintenance-wise
- when it was just derived from (or the same as) posix_sitl_default,
I think.

cmake/configs/posix_sitl_broadcast.cmake

@@ -1,92 +1,3 @@
-include(posix/px4_impl_posix)
+include(cmake/configs/posix_sitl_default.cmake)
 
-set(CMAKE_TOOLCHAIN_FILE ${PX4_SOURCE_DIR}/cmake/toolchains/Toolchain-native.cmake)
-
-set(config_module_list
-	drivers/device
-	drivers/boards/sitl
-	drivers/pwm_out_sim
-	platforms/common
-	platforms/posix/px4_layer
-	platforms/posix/work_queue
-	platforms/posix/drivers/adcsim
-	platforms/posix/drivers/gpssim
-	drivers/gps
-	platforms/posix/drivers/tonealrmsim
-	platforms/posix/drivers/accelsim
-	platforms/posix/drivers/airspeedsim
-	platforms/posix/drivers/barosim
-	platforms/posix/drivers/gyrosim
-	platforms/posix/drivers/rgbledsim
-	platforms/posix/drivers/ledsim
-	systemcmds/param
-	systemcmds/mixer
-	systemcmds/ver
-	systemcmds/esc_calib
-	systemcmds/reboot
-	systemcmds/topic_listener
-	systemcmds/perf
-	modules/uORB
-	modules/param
-	modules/systemlib
-	modules/systemlib/mixer
-	modules/sensors
-	modules/simulator
-	modules/mavlink
-	modules/attitude_estimator_q
-	modules/position_estimator_inav
-	modules/local_position_estimator
-	modules/ekf2
-	modules/position_estimator_inav
-	modules/navigator
-	modules/vtol_att_control
-	modules/mc_pos_control
-	modules/mc_att_control
-	modules/mc_pos_control_multiplatform
-	modules/mc_att_control_multiplatform
-	modules/land_detector
-	modules/fw_att_control
-	modules/fw_pos_control_l1
-	modules/dataman
-	modules/sdlog2
-	modules/logger
-	modules/commander
-	lib/controllib
-	lib/mathlib
-	lib/mathlib/math/filter
-	lib/conversion
-	lib/ecl
-	lib/external_lgpl
-	lib/geo
-	lib/geo_lookup
-	lib/launchdetection
-	lib/terrain_estimation
-	lib/runway_takeoff
-	lib/tailsitter_recovery
-	lib/DriverFramework/framework
-	examples/px4_simple_app
-	)
-
-set(config_extra_builtin_cmds
-	serdis
-	sercon
-	)
-
-set(config_sitl_rcS_dir
-	posix-configs/SITL/init/
-	CACHE FILEPATH "init script for sitl"
-	)
-
-set(config_sitl_viewer
-	jmavsim
-	CACHE STRING "viewer for sitl"
-	)
-set_property(CACHE config_sitl_viewer
-	PROPERTY STRINGS "jmavsim;none")
-
-set(config_sitl_debugger
-	disable
-	CACHE STRING "debugger for sitl"
-	)
-set_property(CACHE config_sitl_debugger
-	PROPERTY STRINGS "disable;gdb;lldb")
+# This config is just the same as posix_sitl_default.

cmake/configs/posix_sitl_default.cmake

@@ -97,9 +97,12 @@ set(config_extra_builtin_cmds
 	sercon
 	)
 
+# Default config_sitl_rcS_dir (posix_sitl_default), this is overwritten later
+# for the config posix_sitl_efk2 and set again, explicitly, for posix_sitl_lpe,
+# which are based on posix_sitl_default.
 set(config_sitl_rcS_dir
 	posix-configs/SITL/init/lpe
-	CACHE FILEPATH "init script dir for sitl"
+	CACHE INTERNAL "init script dir for sitl"
 	)
 
 set(config_sitl_viewer

cmake/configs/posix_sitl_ekf2.cmake

@@ -1,5 +1,5 @@
 include(cmake/configs/posix_sitl_default.cmake)
 
 set(config_sitl_rcS_dir
-	posix-configs/SITL/init/ekf2/
+	posix-configs/SITL/init/ekf2
 	)

cmake/configs/posix_sitl_lpe.cmake

@@ -1,5 +1,6 @@
 include(cmake/configs/posix_sitl_default.cmake)
 
+# This is already the default, but lets explicitly set it again to lpe.
 set(config_sitl_rcS_dir
-	posix-configs/SITL/init/lpe/
+	posix-configs/SITL/init/lpe
 	)

cmake/configs/posix_sitl_replay.cmake

@@ -36,6 +36,7 @@ set(config_extra_builtin_cmds
 
 set(config_sitl_rcS_dir
 	posix-configs/SITL/init/replay
+	CACHE INTERNAL "init script dir for sitl"
 	)
 
 set(config_sitl_viewer