Input: wriston - reduce polling frequency

Reduces the polling frequency from 10 Hz to 2 Hz, which should be less a burden
for laptops wrt energy saving. As it is multimedia keys, 500ms (maximum) of
latency should be still fine for the user. In order to keep fluent the feeling
when the user is pressing several keys in a raw (such as changing the volume),
the frequency is increased for a short duration after a key is pressed.

Signed-off-by: Eric Piel <eric.piel@tremplin-utc.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>