V4L/DVB (13633): ir-core: create a new class for remote controllers

Add sysfs skeleton to export remote controller information via
/sys/class/irrcv.

For now, the code doesn't do much. It just exports an attribute that
is meant to  report and control the IR protocol used by the keytable.
However, the callbacks for this new attribute weren't set yet.

Also, it lacks symlinks to the used event interface.

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