V4L/DVB: ir-core: Add support for disabling all protocols

Writing "none" to /dev/class/rc/rc*/protocols will disable all protocols.
This allows an easier setup, from userspace, as userspace applications don't
need to disable protocol per protocol, before enabling a different set of
protocols.

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