[media] bt8xx: fixup RC5 decoding

The bt8xx driver does RC5 decoding for Nebula digi hardware, but includes
some pointless limitations (both start bits must be one, the
device/address/system must be 0x00). Remove those limitations and update
the keymap to use the full RC5 scancode (fortunately the 0x00 address
means that this is perfectly backwards compatible).

Signed-off-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>