power: bms: Report zero SOC if voltage is below cutoff

If the battery voltage remains below the cutoff threshold
for a specific period (determined by a platform data -
vbatt_cutoff_retries) report the SOC as 0. This allows
the userspace to perform a graceful shutdown. Also, provide
a platform data entry (low_voltage_detect) to enable this
functionality.
Enable 'low_voltage_detect' and set 'vbatt_cutoff_retries'
as required to enable the full functionality.

CRs-Fixed: 450387
Change-Id: I668d391cab3d0424fe5f370df0c1169124c34f5e
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>