media: sun6i-csi: Add media ops with link notify callback

In order to keep the power use count fields balanced when link changes
happen between v4l2_pipeline_pm_get/set calls (in open/close),
the link_notify media operation callback needs to be registered.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>