media: vsp1: Adapt entities to configure into a body

Currently the entities store their configurations into a display list.
Adapt this such that the code can be configured into a body directly,
allowing greater flexibility and control of the content.

All users of vsp1_dl_list_write() are removed in this process, thus it
too is removed.

A helper, vsp1_dl_list_get_body0() is provided to access the internal body0
from the display list.

[laurent.pinchart+renesas@ideasonboard.com: Don't remove blank line unnecessarily]

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