HAL_Linux: Enable external clk for RCOutput_Navio
That should fix PWM value drifts.
HAL_Linux: Optimize bandwidth for RCOutput_Navio
40% less bytes in I2C transactions for PCA9685.
AP_HAL_Linux: added LinuxSPIUARTDriver that can handle SPI-driven Ublox
AP_Compass: AK8963 compass (as a part of MPU9250) support

Conflicts:
	libraries/AP_HAL/AP_HAL_Boards.h
AP_Notify: added abstract Led and RGBLed classes