qpnp-fg-gen3: Fix empty SOC handling

Currently, a flag is set when the empty SOC interrupt fires to
indicate SOC 0 to the users. This is not cleared when the battery
voltage goes up. This needs to be fixed. Remove the flag and use
the realtime status of BATT_SOC peripheral to decide it. To make
that even more robust, validate the battery voltage with the
cutoff voltage. While at it, add a print in the driver's probe to
print the battery SOC and voltage. This will be helpful to debug
different battery charging scenarios.

CRs-Fixed: 1086715
Change-Id: Icbbe0d4ab74c6f9bf6f2278a11020a9bc6c41930
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>