power: qpnp-fg-gen4: Add support for SOH calculation

Battery SOH (State of Health) is calculated based on ESR_ACTUAL
and ESR_NOMINAL properties. SOH is calculated based on them and
written back. Add support for it.

Change-Id: Iaa83709dcf066470d9a501c8784d0e72dad3ec8d
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>