media: sun6i-csi: Move power management to runtime pm in capture

Let's just enable the module when we start using it (at stream on)
and benefit from runtime pm instead of enabling it at first open.

Also reorder the call to v4l2_pipeline_pm_get.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>