Rover: need AP_Terrain.h for AP_Mission
Plane: fixed sense of altitude test for glide slope
Tools: add unified device tree overlay to load all requisites

no more loading multiple capes to enable pru, spi, pwm etc. Steps to load the cape during boot also added.
Tools: Remove unrequired pru0 pin setups from BB-PXF-01-00A0 overlay
GCS_MAVLink: ignore alignment warnings in MAVLink headers
Airspeed: fixed example to setup pin
Replay: fixed build
VARTest: fixed build
AP_Math: fixed example build
AP_HAL: fixed example builds
AP_InertialSensor: fixed example build
AC_AttitudeControl: fixed example build
AC_Fence: fixed example build
AC_Sprayer: fixed example build
AC_WPNav: fixed example build
AP_AHRS: fixed example build
AP_Airspeed: fixed example build
AP_BattMonitor: fixed example build
AP_GPS: fixed example build
AP_InertialNav: fixed example build