John's RB fixes for serialrx sbus and spektrum.
Change !NO_CPPM to SERIALRX_CPPM

CPPM is no longer a runtime option, but a compile time option. hence there is a *_CPPM.hex image (just like SPEKTRUM ans SBUS)

SERIALRX_CPPM = use input pin for CPPM_IN (usually ICP)
SERIALRX_SPEKTRUM, SERIALRX_SBUS = use serial port

default channel order (can be changed through program box)
SERIALRX_CPPM = CPPM_RETA1a2F
SERIALRX_SPEKTRUM = CPPM_TAER1a2F
SERIALRX_SBUS = CPPM_AETR1a2F