V4L-DVB: ir-rc5-decoder: Add a decoder for RC-5 IR protocol

This decoder is also based on a state machine, just like the NEC protocol
decoder. It is pedantic in the sense that accepts only 14 bits. As there
are some variants that outputs less bits, it needs to be improved to also
handle those.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>