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 <[e-mail]>
Signed-off-by: Kishon Vijay Abraham I <[e-mail]>

Documentation/devicetree/bindings/phy/qcom-ipq806x-sata-phy.txt

···
+Qualcomm IPQ806x SATA PHY Controller
+------------------------------------
+
+SATA PHY nodes are defined to describe on-chip SATA Physical layer controllers.
+Each SATA PHY controller should have its own node.
+
+Required properties:
+- compatible: compatible list, contains "qcom,ipq806x-sata-phy"
+- reg: offset and length of the SATA PHY register set;
+- #phy-cells: must be zero
+- clocks: must be exactly one entry
+- clock-names: must be "cfg"
+
+Example:
+	sata_phy: sata-phy@1b400000 {
+		compatible = "qcom,ipq806x-sata-phy";
+		reg = <0x1b400000 0x200>;
+
+		clocks = <&gcc SATA_PHY_CFG_CLK>;
+		clock-names = "cfg";
+
+		#phy-cells = <0>;
+	};