dt-bindings: display: mediatek: gamma: Add compatible for MediaTek MT6795

Add a compatible string for MediaTek Helio X10 MT6795's GAMMA block: this
is the same as MT8173.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20230412112739.160376-11-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

Author: AngeloGioacchino Del Regno

Documentation/devicetree/bindings/display/mediatek/mediatek,gamma.yaml

@@ -24,6 +24,10 @@ properties:
       - enum:
           - mediatek,mt8173-disp-gamma
           - mediatek,mt8183-disp-gamma
+      - items:
+          - enum:
+              - mediatek,mt6795-disp-gamma
+          - const: mediatek,mt8173-disp-gamma
       - items:
           - enum:
               - mediatek,mt8186-disp-gamma