media: vsp1: Replace the display list internal flag with a flags field

To prepare for addition of more flags to the display list, replace the
'internal' flag field by a bitmask 'flags' field.

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