boards/modalai: separate voxl2 builds into two board builds instead of single board build with different variants

* Made voxl2 apps processor and slpi dsp processor builds into separate board builds so that they can
more easily be configured independently.

* Removed board specific link library command from px4_config.cmake and moved it to a more generic
board specific solution that can be used by any board that needs custom link libraries.

* Removed redundant cmake command for Qurt

* Removed unused definition from Qurt cmake file

* Removed unnecessary QURT_LIB cmake function

* Reorganized the voxl2 build structure to avoid 4 level board directories.

* Reverted cmake files to remove 4 level board naming code

* Updated documentation

cmake/kconfig.cmake

@@ -34,7 +34,7 @@ if(EXISTS ${BOARD_DEFCONFIG})
     # Depend on BOARD_DEFCONFIG so that we reconfigure on config change
     set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS ${BOARD_DEFCONFIG})
 
-    if(${LABEL} MATCHES "default" OR ${LABEL} MATCHES "qurt" OR ${LABEL} MATCHES "recovery" OR ${LABEL} MATCHES "bootloader" OR ${LABEL} MATCHES "canbootloader")
+    if(${LABEL} MATCHES "default" OR ${LABEL} MATCHES "recovery" OR ${LABEL} MATCHES "bootloader" OR ${LABEL} MATCHES "canbootloader")
         # Generate boardconfig from saved defconfig
         execute_process(COMMAND ${CMAKE_COMMAND} -E env ${COMMON_KCONFIG_ENV_SETTINGS}
                         ${DEFCONFIG_PATH} ${BOARD_DEFCONFIG}
@@ -228,10 +228,6 @@ if(EXISTS ${BOARD_DEFCONFIG})
 
         # platform-specific include path
         include_directories(${PX4_SOURCE_DIR}/platforms/${PX4_PLATFORM}/src/px4/common/include)
-
-        if(PLATFORM STREQUAL "qurt")
-            include(${PX4_SOURCE_DIR}/boards/modalai/voxl2/cmake/voxl2_qurt.cmake)
-        endif()
     endif()
 
 	if(ARCHITECTURE)