[media] btcx-risc: move from media/i2c to media/common

The btcx-risc module is a helper module for bttv/conexant based TV cards.
It isn't an i2c module at all, instead it should be in common since it is
used by 4 pci drivers.

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