regulator: cpr-regulator: add support for per-virtual-corner voltage limits

Add support for per-virtual-corner ceiling and floor voltage
limits to be specified via device tree.  These limits override
the required per-fuse-corner limits also specified via device
tree.

Specifying per-virtual-corner floor voltages allows for further
power savings on chips which can safely operate at lower voltages
for the lower CPU frequenices associated with a given fuse
corner.

Change-Id: I3712bb34a55155780445cbecbd5190e2da31c35a
CRs-Fixed: 721967
Signed-off-by: David Collins <collinsd@codeaurora.org>