regulator: core: Add support for disabling ramp delay

Some hardwares support disabling ramp delay, so adding ramp_disable flag to
constraints. It will be used to figure out whether ramp_delay in constraints
is explicitly set to zero or its unintialized (zero by default).
And we don't need to call set_voltage_time_sel() for regulators for whom ramp
delay is disabled in constraints.

Signed-off-by: Yadwinder Singh Brar <yadi.brar@samsung.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
diff --git a/Documentation/devicetree/bindings/regulator/regulator.txt b/Documentation/devicetree/bindings/regulator/regulator.txt
index 48a3b8e..2bd8f09 100644
--- a/Documentation/devicetree/bindings/regulator/regulator.txt
+++ b/Documentation/devicetree/bindings/regulator/regulator.txt
@@ -12,6 +12,8 @@
 - regulator-allow-bypass: allow the regulator to go into bypass mode
 - <name>-supply: phandle to the parent supply/regulator node
 - regulator-ramp-delay: ramp delay for regulator(in uV/uS)
+  For hardwares which support disabling ramp rate, it should be explicitly
+  intialised to zero (regulator-ramp-delay = <0>) for disabling ramp delay.
 
 Deprecated properties:
 - regulator-compatible: If a regulator chip contains multiple