regulator: regulator framework core

This adds the regulator framework core.

This framework is designed to provide a generic interface to voltage
and current regulators within the Linux kernel. It's intended to
provide voltage and current control to client or consumer drivers and
also provide status information to user space applications through a
sysfs interface.

The intention is to allow systems to dynamically control regulator
output in order to save power and prolong battery life. This applies
to both voltage regulators (where voltage output is controllable) and
current sinks (where current output is controllable).

This framework safely compiles out if not selected so that client
drivers can still be used in systems with no software controllable
regulators.
Signed-off-by: NLiam Girdwood <lg@opensource.wolfsonmicro.com>
Signed-off-by: NGreg Kroah-Hartman <greg@kroah.com>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>