dt-bindings: display: mediatek: ovl: Add compatible strings for MT8188 MDP3

Add compatible strings for the MDP3 OVL hardware components in
MediaTek's MT8188 SoC and it is compatible with the existing
MT8195 MDP OVL components.

Signed-off-by: Jason-JH.Lin <[e-mail]>
Suggested-by: AngeloGioacchino Del Regno <[e-mail]>
Acked-by: Chun-Kuang Hu <[e-mail]>
Reviewed-by: AngeloGioacchino Del Regno <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: AngeloGioacchino Del Regno <[e-mail]>

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

···
               - mediatek,mt8186-disp-ovl
               - mediatek,mt8365-disp-ovl
           - const: mediatek,mt8192-disp-ovl
+      - items:
+          - const: mediatek,mt8188-mdp3-ovl
+          - const: mediatek,mt8195-mdp3-ovl
 
   reg:
     maxItems: 1