Scratch in a mostly-building board config for fmuv2

apps/drivers/boards/px4fmuv2/Makefile

apps/drivers/boards/px4fmuv2/px4fmu_can.c

apps/drivers/boards/px4fmuv2/px4fmu_init.c

apps/drivers/boards/px4fmuv2/px4fmu_internal.h

apps/drivers/boards/px4fmuv2/px4fmu_pwm_servo.c

apps/drivers/boards/px4fmuv2/px4fmu_spi.c

apps/drivers/boards/px4fmuv2/px4fmu_usb.c

apps/drivers/drv_gpio.h

apps/drivers/stm32/drv_hrt.c

apps/sensors/sensors.cpp

makefiles/config_px4fmuv2_default.mk

nuttx/arch/arm/src/stm32/chip/stm32_syscfg.h

nuttx/configs/px4fmuv2/Kconfig

nuttx/configs/px4fmuv2/common/Make.defs

nuttx/configs/px4fmuv2/common/ld.script

nuttx/configs/px4fmuv2/include/board.h

nuttx/configs/px4fmuv2/include/nsh_romfsimg.h

nuttx/configs/px4fmuv2/nsh/Make.defs

nuttx/configs/px4fmuv2/nsh/appconfig

nuttx/configs/px4fmuv2/nsh/defconfig