[media] V4L: pxa-camera: switch to using subdev .s_power() core operation

soc-camera specific .suspend() and .resume() methods are deprecated
and should be replaced by the subdev standard .s_power() operation.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>