mission feasibility checker: add check for waypoint altitude relative to home position altitude
mission feasibility checker: remove audio warning for waypoint below home altitude
mission feasibility checker: add missing default return in checkHomePositionAltitude
romfs: Added back mixer readme, now gets filtered out
Merge branch 'master' of github.com:PX4/Firmware
FMUv1 board prettifying
Enable SPI4 for FMUv2
Add SPI4 init bits for FMUv2
Fix SPI select on port 4 to use the right defines
Count devices on SPI4 / EXT from 1 as for the other buses
Merge pull request #1017 from PX4/spi4_support

SPI4 support
Merge pull request #694 from thomasgubler/beta_homealtitudewarning

mission feasibility checker: add warning if waypoint is below home altitude
Merge pull request #1019 from PX4/beta

mission feasibility checker: add warning if waypoint is below home altitude
Merge branch 'master' into follower