[media] winbond-cir: asynchronous tx

Change winbond-cir's tx support to be asynchronous and not to mess with
the TX buffer. Essentially the winbond-cir counterpart to the patch
Sean Young sent for iguanair.

Signed-off-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>