TradHeli: Configurable RC_SPEED *per each servo* (digital/tail servo compatibility)

#### Issue details
Bigger (700 class) Helicopters uses CCPM (120°) swashplates with specialized, high freq digital servos and can use special, super fast tail servos with different pulse witdth than standard (centered at 760us rather than 1500us).
Since RC_SPEED is a global parameter right now, you cannot use this mixed servo configurations. Either, manually setting RC_SPEED can lead to burn expensive servos.

Pls make per-servo configuration possible, letting mixed freq rates config possible (maybe useful also to other configurations, like quad-plane and so on) and also pls make some preset for "standard size, high performance" helicopter digital servos (333hz, 760us, etc)

#### Version
3.5 trad heli

#### Platform
[ ] All
[ ] AntennaTracker
[ X] Copter
[ ] Plane
[ ] Rover
[ ] Submarine

#### Airframe type
700-class tradheli

#### Hardware type
Pixhawk/Pixhawk2