devicetree/bindings: add reset-gpios and vcc-supply for panel-dpi

Some displays have a reset input and/or need a regulator to function
properly. Allow to specify them for panel-dpi devices.

Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>