The current of_get_display_timings() reads multiple display timings,
allocating memory for the entries. However, most of the time when
parsing display timings from DT data is needed, there's only one display
timing as it's not common for a LCD panel to support multiple videomodes.

This patch creates a new function:

int of_get_display_timing(struct device_node *np, const char *name,
               struct display_timing *dt);

which can be used to parse a single display timing entry from the given
node name.
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Philipp Zabel <p.zabel@pengutronix.de>

This adds support for reading display timings from DT into a struct
display_timings. The of_display_timing implementation supports multiple
subnodes. All children are read into an array, that can be queried.

If no native mode is specified, the first subnode will be used.

For cases where the graphics driver knows there can be only one
mode description or where the driver only supports one mode, a helper
function of_get_videomode is added, that gets a struct videomode from DT.
Signed-off-by: NSteffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: NPhilipp Zabel <p.zabel@pengutronix.de>
Acked-by: NStephen Warren <swarren@nvidia.com>
Reviewed-by: NThierry Reding <thierry.reding@avionic-design.de>
Acked-by: NThierry Reding <thierry.reding@avionic-design.de>
Tested-by: NThierry Reding <thierry.reding@avionic-design.de>
Tested-by: NPhilipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: NAfzal Mohammed <Afzal@ti.com>
Tested-by: NRob Clark <robclark@gmail.com>
Tested-by: NLeela Krishna Amudala <leelakrishna.a@gmail.com>