Input: ati_remote - make button repeat sensitivity configurable

ati_remote causes repeats after only .23 seconds with my remote and
makes it hard to use comfortably. Make a precise way of setting the
repeat delay time in milliseconds and default it to 500ms.  The old
behavior can be had by setting repeat_delay = 0.

Signed-off-by: Karl Pickett <karl.pickett@gmail.com>
Signed-off-by: Vincent Vanackere <vincent.vanackere@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>