power: qpnp-fg-gen3: Add support for software based ESR during charging

On wearable platforms where the FCC supported by the battery is lower
than 300mA (lowest possible FCC for HW ESR) the HW based ESR pulsing
cannot be used.

Add support for SW based ESR where the SW periodically reduces
FCC and enables the FG to extract an ESR. This feature can be
enabled by the DT property  "qcom,fg-use-sw-esr".

Change-Id: Iaf9e1336438eb6f0c75032f99b7def8970508d33
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>