[media] mce_kbd: add encoder

Split the protocol into two variants, one for keyboard and one for mouse
data.

Note that the mce_kbd protocol cannot be used on the igorplugusb, since
the IR is too long.

Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>