RXMSP is no longer a serial rx provider since it uses MSP and not it's
own dedicated serial port.
Added a feature to enable/disable RX_MSP.
Renamed feature SERIALRX to RX_SERIAL.
Renamed feature PARALLEL_PWM to RX_PARALLEL_PWM
Renamed PPM to RX_PPM.

Update serial configuration checking to better support Serial RX and
telemetry by verifiying serial port features and supported baud rates.

It's now possible to use a low-speed serial rx provider via softserial -
only problem is all the current serial rx providers are 100000/115200
baud.  The code changes however open the door for using serial rx and
any capable serial port such as uart3-5 on the STM32F30x

It's also now possible to use GPS at low speeds on software serial
ports.
Latest binaries.