[media] rc-main: add generic scancode filtering

Add generic scancode filtering of RC input events, and fall back to
permitting any RC_FILTER_NORMAL scancode filter to be set if no s_filter
callback exists. This allows raw IR decoder events to be filtered, and
potentially allows hardware decoders to set looser filters and rely on
generic code to filter out the corner cases.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Antti Seppälä <a.seppala@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>