dt-bindings: Add Evervision VGG804821 panel

Add device tree bindings for the Evervision VG804821 800x480 5.0" LCD
TFT parallel panel.
Signed-off-by: NMarco Felsch <m.felsch@pengutronix.de>
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NThierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190416100645.21689-3-m.felsch@pengutronix.de

Documentation/devicetree/bindings/display/panel/evervision,vgg804821.txt

+Evervision Electronics Co. Ltd. VGG804821 5.0" WVGA TFT LCD Panel
+
+Required properties:
+- compatible: should be "evervision,vgg804821"
+- power-supply: See simple-panel.txt
+
+Optional properties:
+- backlight: See simple-panel.txt
+- enable-gpios: See simple-panel.txt
+
+This binding is compatible with the simple-panel binding, which is specified
+in simple-panel.txt in this directory.