PWM and PPM can now coexist in the same load and be
selected at boot time via the hwsettings UAVObject.
This is basically a complete restructuring of the
way the drivers interact with the TIM peripheral in
the STM32.
As a side effect, the PWM and PPM drivers are now
ready to support multiple instances of each.
This also provides the first step toward being able
to reassign some of the PWM input pins to be servo
output pins. Still more work required, but this is
a good start.
This is a port of a work-in-progress by Sambas onto
the new driver infrastructure needed for boot-time
configuration.
PPM and PWM still don't coexist in a build but this
is closer.
All receivers now fall under the same driver API provided
by pios_rcvr.c.
This is part of a larger sequence of commits that will
switch the receiver selection over to boot time dynamic
configuration via UAVObjects.
