media: mt9m114: Factor out mt9m114_configure_pa

The function mt9m114_configure writes the configuration registers of both,
the pixel array (pa) and the image flow processor (ifp).
This is undesirable if only the config of the pa should be changed without
affecting the ifp.

Factor out the function mt9m114_configure_pa() that just writes the
pa-configuration.

Signed-off-by: Mathis Foerst <mathis.foerst@mt.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>