Input: add generic support for sparse keymaps

More and more devices choose to reimplement support for sparse keymaps
first introduced by wistron driver. Move it into a library module so it
can be easily used by interested parties.

Reviewed-by: Anisse Astier <anisse@astier.eu>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
6 files changed