dt-bindings: phy: Add Amlogic A1 USB2 PHY Bindings

Add the Amlogic A1 Family USB2 PHY Bindings

It supports Host mode only.

Signed-off-by: Yue Wang <yue.wang@amlogic.com>
Signed-off-by: Hanjie Lin <hanjie.lin@amlogic.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>