[media] rc-main: allow raw protocol drivers to restrict the allowed protos

On some hardware (au0828/au8522), the hardware is broken with
regards to the initial pulse detection. So, the driver needs to
produce a fake start pulse. That limits the acceptable protocols,
as it is not possible to produce a fake pulse that would cover
all supported protocols.

So, allow the driver to explicitly set the allowed protocols.

If the driver doesn't specify, keep the old behavior.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>