drm/vmwgfx: Add a new interface for plane update on a display unit

Add a new struct vmw_du_update_plane similar to vmw_kms_dirty which
represent the flow of operations needed to update a display unit from
surface or bo (blit a new framebuffer).

v2:
- Kernel doc correction.
- Rebase.

v3: Rebase to new resource validation.

Signed-off-by: Deepak Rawat <drawat@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>