[media] gspca_sonixb: Refactor to unify bridge handling

Refactor the code to unify how the sn9c101/102 and the sn9c103 bridge
are handled. Also move code which is the same for all sensors from
the per sensor init register settings to a central place.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>