[media] bt8xx: make driver routines fit into its own namespcae

There is a few conflicts with older symbols on older kernels so we
have to patch this driver when backporting. Instead just make these
routines specific to the driver.

Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>