Merge FMUv3 into FMUv2

cmake/configs/nuttx_px4fmu-v2_default.cmake

cmake/configs/nuttx_px4fmu-v3_default.cmake

nuttx-configs/px4fmu-v2/scripts/ld_full.script

nuttx-configs/px4fmu-v3/Kconfig

nuttx-configs/px4fmu-v3/include/board.h

nuttx-configs/px4fmu-v3/include/nsh_romfsimg.h

nuttx-configs/px4fmu-v3/nsh/Make.defs

nuttx-configs/px4fmu-v3/nsh/defconfig

nuttx-configs/px4fmu-v3/src/Makefile

nuttx-configs/px4fmu-v3/src/empty.c

src/drivers/boards/px4fmu-v2/CMakeLists.txt

src/drivers/boards/px4fmu-v2/board_config.h

src/drivers/boards/px4fmu-v2/px4fmu_i2c.c

src/drivers/boards/px4fmu-v2/px4fmu_init.c

src/drivers/boards/px4fmu-v2/px4fmu_spi.c

src/drivers/boards/px4fmu-v3/CMakeLists.txt

src/drivers/boards/px4fmu-v3/board_config.h

src/drivers/boards/px4fmu-v3/px4fmu_can.c

src/drivers/boards/px4fmu-v3/px4fmu_init.c

src/drivers/boards/px4fmu-v3/px4fmu_led.c