Fuel Gauge: Add fuel gauging algorithms

FG module takes voltage, current and coulomb counter
readings from the PMIC, executes fuel gauging algorithms,
and outputs estimated battery state of charge to the
sysfs interface.

Change-Id: I182acbdb0bb69380a7452c1b3a99f198031fdf64
Signed-off-by: Max Herman <mherman@fsisys.com>