power: qpnp-fg-gen3: add support to configure low discharge ki coefficients

Currently, ki coefficient for low discharging current can be
configured once based on DT specification. Change it as an
array of values similar to high/medium discharging current ki
coefficients so that they can be configured dynamically based
on SOC thresholds.

Change-Id: Ia8a3e49d92cd60bb85bafbdeac674fdd4168c85c
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>