The previous servo driver didn't provide any benefit over using PWM
directly, as users controlled the servo in terms of PWM duty cycles.
This changes the interface to provide a high level interface that
abstracts the gory PWM details.
In addition, a SAUL layer and auto-initialization is provided.
Co-authored-by: benpicco <benpicco@googlemail.com>
Parameters for servo_init/servo_set are in ms only when using default values for SERVO_RESOLUTION and SERVO_FREQUENCY.
When using non default values, user must scale values to be in the range of [0, SERVO_RESOLUTION]
Signed-off-by: Marc Poulhiès <dkm@kataplop.net>