regulator: cpr3-regulator: add support for corners above max fuse corner

Add support for fuse corner to corner mappings in which the
highest fuse corner is mapped to a corner lower than the
highest corner.  This can be used to define a corner which has
a constant voltage offset above the highest fuse corner but which
does not impact interpolation for the lower corners.

Change-Id: Ie41522cb06ca81898f58458694067a567f608df0
CRs-Fixed: 981475
Signed-off-by: David Collins <collinsd@codeaurora.org>