power: smb1360: Add an API to allocate OTP backup registers

8 pairs of OTP backup registers (from 0xE0 to 0xEF) are provided
in SMB1360 chip to override OTP register values. Add a mechanism
to manage the limited OTP backup registers' usage allocation.
The OTP back up registers could be allocated with pairs and the
total usage allocation count can't exceed the total amount
-- 8 pairs.

CRs-Fixed: 846212
Change-Id: Idd5abba360e35fc4864c9ce9daeab4c2d5555f30
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>
Signed-off-by: Qiang Huang <qianghuang@codeaurora.org>