[media] media: platform: pxa_camera: introduce sensor_call

Introduce sensor_call(), which will be used for all sensor invocations.
This is a preparation move to v4l2 device conversion, ie. soc_camera
adherence removal.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>