media: staging: rkisp1: validate links before powering and streaming

In function rkisp1_vb2_start_streaming, the call to
media_pipeline_start should be the first thing in order
to validate the links and prevents their state from being modified
before power up and streaming.

Adjust stop streaming to the same logic, call media_pipeline_stop
after we disable streaming on the entities in the topology.

Signed-off-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>