media: v4l: vsp1: Generalize detection of entity removal from DRM pipeline

When disabling a DRM plane, the corresponding RPF is only marked as
removed from the pipeline in the atomic update handler, with the actual
removal happening when configuring the pipeline at atomic commit time.
This is required as the RPF has to be disabled in the hardware, which
can't be done from the atomic update handler.

The current implementation is RPF-specific. Make it independent of the
entity type by using the entity's pipe pointer to mark removal from the
pipeline. This will allow using the mechanism to remove BRU instances.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>