V4L/DVB: ir-core: Add support for badly-implemented hardware decoders

A few hardware Remote Controller decoders, even using a standard protocol,
aren't able to provide the entire scancode. Due to that, the capability
of using other IR's are limited on those hardware.

Adds a way to indicate to ir-core what are the bits that the hardware
provides, from a scancode, allowing the addition of a complete IR table
to the kernel and allowing a limited support for changing the Remote
Controller on those devices.

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