dt-bindings: phy: mediatek,dsi-phy: Add support for MT6893

Add support for the MediaTek Dimensity 1200 (MT6893) SoC: the DSI
PHY found in this chip is fully compatible with the one found in
the MT8183 SoC.

Signed-off-by: AngeloGioacchino Del Regno <[e-mail]>
Acked-by: Rob Herring (Arm) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

Documentation/devicetree/bindings/phy/mediatek,dsi-phy.yaml

···
           - const: mediatek,mt8173-mipi-tx
       - items:
           - enum:
+              - mediatek,mt6893-mipi-tx
               - mediatek,mt8188-mipi-tx
               - mediatek,mt8195-mipi-tx
               - mediatek,mt8365-mipi-tx