[media] cx88: Add RC logic for Leadtek PVR 2000

Currently, lirc-i2c has a decoding logic for Leadtek Remote
Control. Move it to cx88, as we intend to remove lirc-i2c.

For now, initialize LIRC remote keytable with RC_MAP_EMPTY, as
we don't know its keymap yet. It would be nice to later check
if is there any file on LIRC userspace with that keytable.

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