msm: msm-batt: Add the fail-safe voltage.

Failsafe voltage is the minimum operating voltage for msm battery.
This change adds code to handle this voltage in battery driver, to
fecilitate graceful shutdown when this level is reached.

CRs-Fixed: 366506
Change-Id: Iedc2ed603b0c7448e6da31b169ee1746c723d69d
Signed-off-by: Krishna Vanka <kvanka@codeaurora.org>