[media] rc: ir-rc6-decoder: Add encode capability

Add the capability to encode RC-6 and RC-6A scancodes as raw events.
The protocol is chosen based on the specified protocol mask, and
whether all the required bits are set in the scancode mask, and none of
the unused bits are set in the scancode data.

The Manchester modulation helper is used several times with various
timings so that RC-6 header preamble, the header, header trailing bit
and the data itself can be modulated correctly.

Signed-off-by: Antti Seppälä <a.seppala@gmail.com>
Cc: James Hogan <james@albanarts.com>
Cc: David Härdeman <david@hardeman.nu>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>