drm: msm: dsi: Update DSI parser util to skip disabled child nodes

Currently, disabled timing child nodes or power supply nodes are
not skipped because of which status = "disabled" entry does not
work for child nodes. Use of_get_next_available_child to skip
disabled child nodes.

Change-Id: Ib6e4b655f83dd0ee3ffddd496976c34030fa3dc0
Signed-off-by: Ritesh Kumar <riteshk@codeaurora.org>