dt-bindings: phy: convert HDMI PHY binding to YAML schema

Convert HDMI PHY binding to YAML schema mediatek,hdmi-phy.yaml

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Cc: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://lore.kernel.org/r/20201225075258.33352-6-chunfeng.yun@mediatek.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>