V4L/DVB: ir-core: properly present the supported and current protocols

Hardware decoders have a more limited set of decoders than software ones.
In general, they support just one protocol at a given time, but allow
changing between a few options.

Rename the previous badly named "current_protocol" as just "protocol",
meaning the current protocol(s) accepted by the driver, and
add a "support_protocols" to represent the entire universe of supported
protocols by that specific hardware.

As commented on http://lwn.net/Articles/378884/

, the "one file, one value"
rule doesn't fit nor does make much sense for bitmap or enum values. So, the
supported_protocols will enum all supported protocols, and the protocol
will present all active protocols.

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