media: subdev: add stream based configuration

Add support to manage configurations (format, crop, compose) per stream,
instead of per pad. This is accomplished with data structures that hold
an array of all subdev's stream configurations.

The number of streams can vary at runtime based on routing. Every time
the routing is changed, the stream configurations need to be
re-initialized.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>