[media] v4l: vsp1: Consolidate entity ops in a struct vsp1_entity_operations

Entities have two operations, a destroy operation stored directly in
vsp1_entity and a set_memory operation stored in a vsp1_rwpf_operations
structure. Move the two to a more generic vsp1_entity_operations
structure that will serve to implement additional operations.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>