media: staging: rkisp1: cap: refactor enable/disable stream to allow multistreaming

Allow streaming from self picture path and main picture path at the same
time.

Take care for s_stream() callbacks to not be called twice.
When starting a stream, s_stream(true) shouldn't be called for the isp
and the sensor if the other stream is already enabled (since it was
already called).
When stopping a stream, s_stream(false) shouldn't be called for isp and
the sensor if the other stream is still enabled.

Remove the callback function scheme for navigating through the topology,
simplifying the code, improving readability.

Remove multistreaming item from the TODO list.

Signed-off-by: Helen Koike <helen.koike@collabora.com>
Reviewed-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>