regulator: s5m8767: Document new binding for Buck9 GPIO control

Add documentation for new binding for controlling (enable/disable) the
Buck9 Converter by GPIO (BUCK9EN).
Signed-off-by: NKrzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

Documentation/devicetree/bindings/regulator/s5m8767-regulator.txt

@@ -69,13 +69,16 @@ sub-node should be of the format as listed below.
 		};
 	};
 The above regulator entries are defined in regulator bindings documentation
-except op_mode description.
+except these properties:
 	- op_mode: describes the different operating modes of the LDO's with
 		power mode change in SOC. The different possible values are,
 		0 - always off mode
 		1 - on in normal mode
 		2 - low power mode
 		3 - suspend mode
+	- s5m8767,pmic-ext-control-gpios: (optional) GPIO specifier for one
+		GPIO controlling this regulator (enable/disable); This is
+		valid only for buck9.
 
 The following are the names of the regulators that the s5m8767 pmic block
 supports. Note: The 'n' in LDOn and BUCKn represents the LDO or BUCK number
@@ -148,5 +151,13 @@ Example:
 				regulator-always-on;
 				regulator-boot-on;
 			};
+
+			vemmc_reg: BUCK9 {
+				regulator-name = "VMEM_VDD_2.8V";
+				regulator-min-microvolt = <2800000>;
+				regulator-max-microvolt = <2800000>;
+				op_mode = <3>; /* Standby Mode */
+				s5m8767,pmic-ext-control-gpios = <&gpk0 2 0>;
+			};
 		};
 	};