[media] gcpca_sn9c20x: Convert to the control framework

HdG: Small fix: don't register some controls for sensors which don't
have an implementation for them.

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