[media] rc-core: merge rc5 and streamzap decoders

Now that the protocol is part of the scancode, it is pretty easy to merge
the rc5 and streamzap decoders. An additional advantage is that the decoder
is now stricter as it waits for the trailing silence before determining that
a command is a valid rc5/streamzap command (which avoids collisions that I've
seen with e.g. Sony protocols).

Signed-off-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>