dt-bindings: display: mediatek: dsi: Convert dsi_dtbinding to .yaml

Convert mediatek,dsi.txt to mediatek,dsi.yaml format

Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20220504091923.2219-2-rex-bc.chen@mediatek.com/


Signed-off-by: Xinlei Lee <xinlei.lee@mediatek.com>
Signed-off-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>