dt-bindings: phy: Add compatible for Mediatek MT8186

This commit adds dt-binding documentation of T-Phy for Mediatek MT8186 SoC
Platform.

Signed-off-by: Allen-KH Cheng <Allen-KH.Cheng@mediatek.com>
Link: https://lore.kernel.org/r/20220128062050.23978-6-allen-kh.cheng@mediatek.com


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