PM / OPP: Add new bindings to address shortcomings of existing bindings

Current OPP (Operating performance point) device tree bindings have been
insufficient due to the inflexible nature of the original bindings. Over
time, we have realized that Operating Performance Point definitions and
usage is varied depending on the SoC and a "single size (just frequency,
voltage) fits all" model which the original bindings attempted and
failed.

The proposed next generation of the bindings addresses by providing a
expandable binding for OPPs and introduces the following common
shortcomings seen with the original bindings:

- Getting clock/voltage/current rails sharing information between CPUs.
  Shared by all cores vs independent clock per core vs shared clock per
  cluster.

- Support for specifying current levels along with voltages.

- Support for multiple regulators.

- Support for turbo modes.

- Other per OPP settings: transition latencies, disabled status, etc.?

- Expandability of OPPs in future.

This patch introduces new bindings "operating-points-v2" to get these problems
solved. Refer to the bindings for more details.

We now have multiple versions of OPP binding and only one of them should
be used per device.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>