Add a 'menuconfig' target that makes it possible to use the NuttX menuconfig tool on the PX4 config files.
Remove our depdenency on CONFIG_ARCH_BOARD_* coming from <nuttx/config.h>
Clean the FMUv1 config through menuconfig.
NuttX is confused when it doesn't know what board it's building for - since we don't tell it in the config anymore, we need to pass it a hint.
Fix handling of board config files. Treat CONFIG_BOARD like CONFIG_ARCH in the toolchain configuration.
Stop expecting CONFIG_HRT_anything since we aren't baking it into the NuttX config anymore.
Merge pull request #355 from PX4/kconfig-cleanup

Kconfig cleanup