regulator: added support for suspend states

Some systems need to set regulators to specific states when they enter
low power modes, especially around CPUs. There are many of these modes
depending on the particular runtime state.

Currently the regulator consumers are not granted permission to change
suspend state of regulator devices, the constraints are configured at
startup.  In order to allow changes in a vlotage range, we need to add
new properties for voltage range and a flag to give permission to
change the suspend voltage and suspend on/off in suspend mode.

Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>