[media] V4L: mt9m111: switch to v4l2-subdev .s_power() method

Eliminate soc-camera specific .suspend() and .restore() methods in favour
of the standard v4l2-subdev .s_power() method

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>