This will copy the ROMFS into the build directory under etc/, and thus needs a change of the PX4 startup parameters and mixer paths.
- 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