twl6030 battery: use gas gauge for capacity estimation

Use the gas gauge in twl6030 to estimate the remaining battery
capacity.

At bootup, we use an estimate of initial capacity using the measured
battery voltage at bootup. From that point on, all future battery
capacity estimations are done by using the gas gauge to measure
all addition/removal of charge from the battery.

Clamp battery value to 99% if the measured value exceeds 99%.
A later patch will add the code to update the initial estimate
once the battery is fully charged.

TODO: Minimum safe battery voltage reporting needs to be worked on

Change-Id: Iab157b559f9de432a93664e8d78c003af3c75b67
Signed-off-by: Sivakumar Pothireddy <sivakumar.pothireddy@ti.com>
Signed-off-by: Anand Gadiyar <gadiyar@ti.com>