media: lirc: use kfifo rather than lirc_buffer for raw IR

Since the only mode lirc devices can handle is raw IR, handle this
in a plain kfifo.

Remove lirc_buffer since this is no longer needed.

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