power: qpnp-fg: Reconfigure SW_CC_SOC to reduce error

SW_CC_SOC can accumulate error during charging depending on
various conditions. Reset SW_CC_SOC to a full value during
charge termination and to a value calculated based on battery
SOC when the device enters from charging to discharging status.
This will keep SW_CC_SOC to have an accurate value.

While at it, simplify reading SW_CC_SOC by using sign extension
API to avoid confusion.

Change-Id: I64fd1719c704d51ea68b81cded50ef8e4dd4b605
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>