regulator: da9211: Document allowed modes

This patch adds a description of how operating modes may be specified.
Signed-off-by: Anand K Mistry <amistry@google.com>
Link: https://lore.kernel.org/r/20200702131350.2.I6131e251d13f60d8c5347bb4faa9dc2364c87848@changeidSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/da9211.txt

@@ -15,6 +15,8 @@ Required properties:
 Optional properties:
 - enable-gpios: platform gpio for control of BUCKA/BUCKB.
 - Any optional property defined in regulator.txt
+  - regulator-initial-mode and regulator-allowed-modes may be specified using
+    mode values from dt-bindings/regulator/dlg,da9211-regulator.h
 
 Example 1) DA9211
 	pmic: da9211@68 {
@@ -30,6 +32,8 @@ Example 1) DA9211
 				regulator-min-microamp 	= <2000000>;
 				regulator-max-microamp 	= <5000000>;
 				enable-gpios = <&gpio 27 0>;
+				regulator-allowed-modes = <DA9211_BUCK_MODE_SYNC
+							   DA9211_BUCK_MODE_AUTO>;
 			};
 		};
 	};