phy: qcom: Add device tree bindings for IPQ806x SATA PHY

Add binding spec for Qualcomm SoC PHYs, starting with the SATA PHY on
the IPQ806x family of SoCs.

Signed-off-by: Kumar Gala <galak@codeaurora.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>