regulator: cpr3-regulator: Add closed-loop CPR3 support

Add support in the cpr3-regulator driver to configure CPR3
controller registers.  This allows the supply rail to operate
in CPR closed-loop mode in which the CPR hardware is active.

For HMSS CPR3 controllers, also add support for CPR hardware
closed-loop mode.  Hardware closed-loop mode operates the same
way as software closed-loop mode except that CPR up/down voltage
stepping recommendations are handled completely in hardware.
Software does not receive any CPR interrupts when using hardware
closed-loop mode.

Change-Id: I67d13695bc82fbcfac8037990ab476ff76822235
Signed-off-by: David Collins <collinsd@codeaurora.org>