power: qpnp-bms: report charge_counter as a power supply property

Using the internal coulomb counter, report the
POWER_SUPPLY_PROP_CHARGE_COUNTER property in the BMS power supply.

This property can be used to measure average current draw from the
battery.

Change-Id: I01074fc781f6fef53e61288e8ecf6e6ac0af184f
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>