dt-bindings: regulator: add refgen regulator bindings

Some Qualcomm Technologies, Inc. SoCs such as SDM845 utilize
reference bias generators for various internal PHY blocks.
These are called REFGENs.  Add binding documentation for
REFGEN devices.

This is a snapshot from msm-4.19
commit e5cf0a03c6aa ("dt-bindings: regulator: add refgen
regulator bindings").

Change-Id: I9efbea760ba0b07544549d0e28692e386d0c4350

bindings/regulator/qcom,refgen.txt

@@ -0,0 +1,40 @@
+Qualcomm Technologies, Inc. REFGEN Regulator
+
+Some Qualcomm Technologies, Inc. SoCs utilize reference bias generators for
+various internal PHY blocks.  These are called REFGENs.
+
+Supported properties:
+- compatible
+	Usage:      required
+	Value type: <string>
+	Definition: Must be one of: "qcom,refgen-regulator",
+		    "qcom,refgen-sdm845-regulator", or
+		    "qcom,refgen-kona-regulator".
+
+- reg
+	Usage:      required
+	Value type: <prop-encoded-array>
+	Definition: Address and size of the REFGEN registers.
+
+- regulator-name
+	Usage:      required
+	Value type: <string>
+	Definition: Specifies the name for this REFGEN regulator.
+
+- regulator-enable-ramp-delay
+	Usage:      optional
+	Value type: <u32>
+	Definition: REFGEN enable time in microseconds.
+
+- parent-supply
+	Usage:      optional
+	Value type: <phandle>
+	Definition: phandle to the parent supply/regulator node if one exists.
+
+Example:
+
+refgen-regulator@ff1000 {
+	compatible = "qcom,refgen-regulator";
+	reg = <0xff1000 0x60>;
+	regulator-name = "refgen";
+};