power: avs: Add support for CPR (Core Power Reduction)

RBCPR (RapidBridge Core Power Reduction) is a technology to reduce
core power on a CPU or other device. It reads voltage settings in
efuse from product test process as initial settings and populates OPPs
for the device being "monitored". Each OPP corresponds to a "corner"
that has a range of valid voltages for a particular frequency. While
the device is running at a particular frequency, CPR monitors dynamic
factors such as temperature, etc. and adjusts the voltage for that
frequency accordingly to save power and meet silicon characteristic
requirements.

This driver is based on work by others on codeaurora.org[1].

TODO:
* DT binding documentation

[1] https://www.codeaurora.org/cgit/quic/la/kernel/msm-3.10/tree/drivers/regulator/cpr-regulator.c?h=msm-3.10



Cc: David Collins <collinsd@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>