conf: iterate video model children in parent function

conf: iterate video model children in parent function

Previously, we were passing the video "model" node to the "acceleration"
and "resolution" parsing functions and requiring them to iterate over
the children to discover and parse the appropriate node. It makes more
sense to move this responsibility up to the parent function and just
pass these functions the node that needs to be parsed.

Reviewed-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>