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: NH Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: NDaniel Mack <daniel@caiaq.de>
Signed-off-by: NDmitry Torokhov <dtor@mail.ru>

This patch adds a generic driver for rotary encoders connected to GPIO
pins of a system. It relies on gpiolib and generic hardware irqs. The
documentation that also comes with this patch explains the concept and
how to use the driver.
Signed-off-by: NDaniel Mack <daniel@caiaq.de>
Tested-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: NDmitry Torokhov <dtor@mail.ru>