media: mtk-cir: only allow protocols that have software decoders

RC_PROTO_BIT_ALL includes protocols like unknown and other that do not
have IR decoders by definition. If these protocols are set in the
allowed_protocols, they will show in the protocols sysfs file but cannot
be enabled.

Signed-off-by: Sean Young <sean@mess.org>
Acked-by: Sean Wang <sean.wang@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>