mfd: Add bcm590xx pmu DT binding

Add a DT binding for the BCM590xx PMUs. The binding inherits from
the generic regulator bindings.
Signed-off-by: NMatt Porter <mporter@linaro.org>
Reviewed-by: NTim Kryger <tim.kryger@linaro.org>
Reviewed-by: NMarkus Mayer <markus.mayer@linaro.org>
Signed-off-by: NLee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/bcm590xx.txt

+-------------------------------
+BCM590xx Power Management Units
+-------------------------------
+
+Required properties:
+- compatible: "brcm,bcm59056"
+- reg: I2C slave address
+- interrupts: interrupt for the PMU. Generic interrupt client node bindings
+  are described in interrupt-controller/interrupts.txt
+
+------------------
+Voltage Regulators
+------------------
+
+Optional child nodes:
+- regulators: container node for regulators following the generic
+  regulator binding in regulator/regulator.txt
+
+  The valid regulator node names for BCM59056 are:
+  	rfldo, camldo1, camldo2, simldo1, simldo2, sdldo, sdxldo,
+	mmcldo1, mmcldo2, audldo, micldo, usbldo, vibldo,
+	csr, iosr1, iosr2, msr, sdsr1, sdsr2, vsr
+
+Example:
+	pmu: bcm59056@8 {
+		compatible = "brcm,bcm59056";
+		reg = <0x08>;
+		interrupts = <GIC_SPI 215 IRQ_TYPE_LEVEL_HIGH>;
+		regulators {
+			rfldo_reg: rfldo {
+				regulator-min-microvolt = <1200000>;
+				regulator-max-microvolt = <3300000>;
+			};
+
+			...
+		};
+	};