regulator: of: add property for allowed modes specification

Add a common device tree property for regulator nodes to support
the specification of allowed operating modes.
Signed-off-by: David Collins <collinsd@codeaurora.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/regulator.txt

@@ -59,6 +59,11 @@ Optional properties:
 - regulator-initial-mode: initial operating mode. The set of possible operating
   modes depends on the capabilities of every hardware so each device binding
   documentation explains which values the regulator supports.
+- regulator-allowed-modes: list of operating modes that software is allowed to
+  configure for the regulator at run-time.  Elements may be specified in any
+  order.  The set of possible operating modes depends on the capabilities of
+  every hardware so each device binding document explains which values the
+  regulator supports.
 - regulator-system-load: Load in uA present on regulator that is not captured by
   any consumer request.
 - regulator-pull-down: Enable pull down resistor when the regulator is disabled.