msm: cpr-regulator: make cpr-enable specific for corners

When a corner's ceiling and floor voltages are same, there is no
need to enable CPR at all. Add code to handle such case.

Change-Id: Ib0af4ab00eda7c933a9c26b0ea7be1e8aa06eb3e
Signed-off-by: Willie Ruan <wruan@codeaurora.org>