V4L/DVB: staging/lirc: add lirc_imon driver

Nb: this is a very trimmed-down lirc_imon, which only supports the
oldest generation of imon devices that don't do onboard signal decoding
like the most recent generation imon devices -- those are now supported
by the ir-core imon driver.

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