dt-bindings: phy: Add compatible for Mediatek MT8188

Add dt-binding documentation of dsi-phy for MediaTek MT8188 SoC.

Signed-off-by: Shuijing Li <shuijing.li@mediatek.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230908075310.17825-1-shuijing.li@mediatek.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>