PM / OPP: Add ti-opp-supply driver

PM / OPP: Add ti-opp-supply driver

Introduce a ti-opp-supply driver that will use new multiple regulator
support that is part of the OPP core This is needed on TI platforms like
DRA7/AM57 in order to control both CPU regulator and Adaptive Body Bias
(ABB) regulator. These regulators must be scaled in sequence during an
OPP transition depending on whether or not the frequency is being scaled
up or down.

This driver also implements AVS Class0 for these parts by looking up the
required values from registers in the SoC and programming adjusted
optimal voltage values for each OPP.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>