power: qpnp-fg: Expose coulomb counter via charge_counter property

Currently, charge_now property is exposing coulomb counter only
when the capacity learning is in progress. Expose it through
charge_counter property so that it can be used for profiling.

Change-Id: Id36060e5edaf134c13b62cf36cbdb3746e8d68d7
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>