dt-bindings: panel: Add compatible for Xingbangda XBD599 panel

Xingbangda XBD599 is a 5.99" 720x1440 MIPI-DSI LCD panel. It is based on
Sitronix ST7703 LCD controller just like rocktech,jh057n00900. It is
used in PinePhone.

Add a compatible for it.
Signed-off-by: NOndrej Jirman <megous@megous.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200701162928.1638874-4-megous@megous.com

Documentation/devicetree/bindings/display/panel/rocktech,jh057n00900.yaml

@@ -18,7 +18,11 @@ allOf:
 
 properties:
   compatible:
-    const: rocktech,jh057n00900
+    enum:
+        # Rocktech JH057N00900 5.5" 720x1440 TFT LCD panel
+      - rocktech,jh057n00900
+        # Xingbangda XBD599 5.99" 720x1440 TFT LCD panel
+      - xingbangda,xbd599
 
   reg:
     maxItems: 1