[media] adv7180: Cleanup register define naming

Consistently prefix register defines with ADV7180_REG. Also remove the "ADI"
from register names, the ADV7180 prefix should provide enough of a namespace
separation.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Federico Vaga <federico.vaga@gmail.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>