power: qpnp-bms: allow additional corrections in low voltage

When the battery is in the low voltage region, allow corrections
even when the SoC estimate is higher than 15. This case can occur
in low temperature cases where it's necessary to correct SoC very
quickly. For example, in -20 degrees celsius, the battery internal
resistance is very large (1 to 1.5 Ohms). A small change in current
can make a huge change in SoC. There has been times where SoC needs
to be corrected from 70% to 0 very quickly, and the BMS driver cannot
wait until the soc estimate goes below 15% to do so.

Additionally, when in the low temperature region, allow more SoC
change per second in order to keep up with the large SoC adjustments.

Change-Id: I921d4e8f6ed7e739bade13eecdf67ef0317b326b
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>