dt-bindings: phy: Add Qualcomm Synopsys High-Speed USB PHY binding

It adds bindings for Synopsys 28nm femto phy controller that supports
LS/FS/HS usb connectivity on Qualcomm chipsets.

Changes for v3:
 - Use SoC specific compatible "qcom,qcs404-usb-hsphy".
 - Use OF graph instead of extcon bindings to model the link to USB
   connector.

Changes for v2:
 - Add a pointer to phy/phy-bindings.txt for property #phy-cells.

Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>
Signed-off-by: Anu Ramanathan <anur@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>