dt-bindings: phy: Document Samsung UFS PHY bindings

This patch documents Samsung UFS PHY device tree bindings

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alim Akhtar <alim.akhtar@samsung.com>
Tested-by: Paweł Chmiel <pawel.mikolaj.chmiel@gmail.com>
Link: https://lore.kernel.org/r/20200716192217.35740-1-alim.akhtar@samsung.com


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