Some regulators can run on different operating modes (opmodes). This
allows systems to choose the most efficient opmode for each regulator.

This patch builds on top of (291d761 regulator: Document binding for
regulator suspend state for PM state) adding a regulator-initial-mode
DT property to configure at startup the operating mode for regulators
that support changing its mode during normal operation and a property
regulator-mode to be used in the regulator-state-[mem/disk] nodes for
regulators that supports changing its operating mode when the system
enters in a suspend state.

The set of possible modes that a regulator can operate depends on the
hardware capabilities so a list of generic operating modes can't be
provided. Instead, each hardware binding should define the list of
valid operating modes for the regulators found on that device.
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Mark Brown <broonie@kernel.org>