cmake merge linux cross compile targets (cross + native) and cleanup

- consolidate cross and native variants (only a single default is needed)
   - beaglebone_blue_cross + beaglebone_blue_native => beaglebone_blue_default
   - emlid_navio2_cross + emlid_navio2_native => emlid_navio2_default
   - px4_raspberrypi_cross + px4_raspberrypi_native => px4_raspberrypi_default
 - move upload helpers to cmake/upload.cmake

boards/px4/raspberrypi/default.cmake

@@ -0,0 +1,86 @@
+
+px4_add_board(
+	VENDOR px4
+	MODEL raspberrypi
+	LABEL default
+	PLATFORM posix
+	ARCHITECTURE cortex-a53
+	TOOLCHAIN arm-linux-gnueabihf
+	TESTING
+	DRIVERS
+		#barometer # all available barometer drivers
+		barometer/ms5611
+		batt_smbus
+		camera_capture
+		camera_trigger
+		differential_pressure # all available differential pressure drivers
+		distance_sensor # all available distance sensor drivers
+		gps
+		#imu # all available imu drivers
+		imu/mpu9250
+		linux_pwm_out
+		linux_sbus
+		#magnetometer # all available magnetometer drivers
+		magnetometer/hmc5883
+		pwm_out_sim
+		rpi_rc_in
+		#telemetry # all available telemetry drivers
+	MODULES
+		airspeed_selector
+		attitude_estimator_q
+		battery_status
+		camera_feedback
+		commander
+		dataman
+		ekf2
+		events
+		fw_att_control
+		fw_pos_control_l1
+		land_detector
+		landing_target_estimator
+		load_mon
+		local_position_estimator
+		logger
+		mavlink
+		mc_att_control
+		mc_pos_control
+		mc_rate_control
+		#micrortps_bridge
+		navigator
+		rc_update
+		rover_pos_control
+		sensors
+		sih
+		#simulator
+		vmount
+		vtol_att_control
+	SYSTEMCMDS
+		dyn
+		esc_calib
+		led_control
+		mixer
+		motor_ramp
+		param
+		perf
+		pwm
+		reboot
+		sd_bench
+		shutdown
+		tests # tests and test runner
+		top
+		topic_listener
+		tune_control
+		ver
+		work_queue
+	EXAMPLES
+		bottle_drop # OBC challenge
+		dyn_hello # dynamically loading modules example
+		fixedwing_control # Tutorial code from https://px4.io/dev/example_fixedwing_control
+		hello
+		#hwtest # Hardware test
+		#matlab_csv_serial
+		px4_mavlink_debug # Tutorial code from http://dev.px4.io/en/debug/debug_values.html
+		px4_simple_app # Tutorial code from http://dev.px4.io/en/apps/hello_sky.html
+		rover_steering_control # Rover example app
+		uuv_example_app
+	)