Input: sh_keysc - switch to using bitmaps

Use bitmaps instead of using 32-bit integers to keep track of the key
states. With this change in place the driver supports key pads with
more than 32 keys.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>