power: qpnp-fg-gen4: Add support for SW based SOC scaling

On aged batteries, SOC calculated by FG can remain high for low Vbatt.
Add support for SW based SOC scaling using filtered battery voltage so
that SOC can be shown to the user in a better way. SW based SOC scaling
is enabled based on DT property and once the Vbatt goes below the specified
threshold.

Change-Id: Idd94fdebab4def6ab53b317efbc67d5a7464a99e
Signed-off-by: Sahil Chandna <chandna@codeaurora.org>