Navio: RCOutput fix, RCOutput optimization, RGB LED support, LinuxSPIUARTDriver for U-blox

External clocking for PCA9685 solves the issue with PWM values drifting.
I2C bandwidth required for PCA9685 is reduced by 40% by writing only falling edge bytes.
Added support for RGB LED on Navio, in order to avoid copypasting PX4 code parts of AP_Notify have been rewritten.
Added LinuxSPIUARTDriver which allows to work with U-blox over SPI. Currently, using internal GPS does not allow to use external GPS on Navio, but the solution for that is on it's way.