power: smb1360: Add delta_soc IRQ handler

Report every change in SOC by registering the delta_soc_handler.
This IRQ is disabled when system suspends.

Also, improve the accuracy of SOC reporting.

CRs-Fixed: 655974
Change-Id: If14d0bb62acbfa537870273f1b8f36fe245cb1f9
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>