media: rkisp1: Move sensor .s_stream() call to ISP

Move the calls to the active sensor's .s_stream() operation to the ISP
subdev's .s_stream(). This groups all handling of the active sensor in
one place, preparing for a rework of that code.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Dafna Hirschfeld <dafna@fastmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>