power: qpnp-fg-gen4: Add CHARGE_NOW property

Add POWER_SUPPLY_PROP_CHARGE_NOW property to expose the initial
capacity when the capacity learning has begun.

CRs-Fixed: 2382855
Change-Id: Ic9cf0251f8bef2f05a6f0b0d5cfe31414d3da2b8
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>