Input: i8042 - allow installing platform filters for incoming data

Some hardware (such as Dell laptops) signal a variety of events through
the i8042 controller, even if these don't map to keyboard events. Add
support for drivers to filter the i8042 event stream in order to respond
to these events and (if appropriate) block them from entering the input
stream.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>