dt-bindings: display/panel: ilitek,ili9881c: describe Waveshare panel

Describe Waveshare 7" DSI panel which uses ILI9881 as a panel
controller. This panel requires two voltags supplies, so add separate
iovcc supply.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Link: https://patch.msgid.link/20260418-waveshare-dsi-touch-v4-1-b249f3e702bd@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>

Documentation/devicetree/bindings/display/panel/ilitek,ili9881c.yaml

@@ -24,6 +24,7 @@ properties:
           - raspberrypi,dsi-7inch
           - startek,kd050hdfia020
           - tdo,tl050hdv35
+          - waveshare,7.0-dsi-touch-a
           - wanchanglong,w552946aaa
           - wanchanglong,w552946aba
       - const: ilitek,ili9881c
@@ -34,6 +35,7 @@ properties:
   backlight: true
   port: true
   power-supply: true
+  iovcc-supply: true
   reset-gpios: true
   rotation: true