power: qpnp-qg: Add termination-current based SOC scaling (TCSS)

Termination current based SOC scaling (TCSS) makes sure that the
SOC converges to 100% at the specified QG-termination current.
TCSS uses a weighted average of the actual battery-current
and the specified termination-current to fit the SOC curve.

Change-Id: I2388d9b6c8fa480c8c18d0a72c1ff773d51e5bcb
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>