[media] cx88: remove dependency on btcx-risc

btcx-risc is for the bt8xx driver and other drivers shouldn't depend
on it. There is no benefit to use that module just to do a
pci_zalloc_consistent.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>