regulator: cpr-regulator: add support for CPR ceiling voltage reduction

Add support for a pair of device tree properties which specify
if the CPR ceiling voltage may be reduced to either the per-fuse-
corner initial voltage fuse value or the per-virtual-corner
interpolated initial voltage value (i.e. the open-loop voltage).

These properties can be used to save power on targets where the
closed-loop settled CPR voltage never needs to exceed the
open-loop initial voltage.

Change-Id: I359b6d8e0c98f4b7f00f7bd90efc72c2aa3865a7
Signed-off-by: David Collins <collinsd@codeaurora.org>