PWM-locked support not properly working after "PWM/Phase"-locked merge

There's a serious functionality, probably also performance, issue caused by the runtime selection patch that did away with the preprocessor #define based switch between "PWM locked" and "phase locked" waveform modes.

See `libraries/Servo/src/Servo.cpp`, in `Servo::attach`, `Servo::detach`, `Servo::writeMicroseconds` the conditional compilation cannot occur.
