V4L/DVB: ir-core: dynamically load the compiled IR protocols

Instead of hardcoding the protocols into ir-core, add a register interface
for the IR protocol decoders, and convert ir-nec-decoder into a client of
ir-core.

With this approach, it is possible to dynamically load the needed IR protocols,
and to add a RAW IR interface module, registered as one IR raw protocol decoder.

This patch opens a way to register a lirc_dev interface to work as an userspace
IR protocol decoder.

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