Input: rotary_encoder - add support for REL_* axes

The rotary encoder driver only supports returning input events
for ABS_* axes, this adds support for REL_* axes.  The relative
axis input event is reported as -1 for each counter-clockwise
step and +1 for each clockwise step.

The ability to clamp the position of ABS_* axes between 0 and
a maximum of "steps" has also been added.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>