power: qpnp-fg-gen4: add TTF/TTE support

Add support for TTF (time to full) and TTE (time to empty) in
GEN4 FG through the following properties.

- POWER_SUPPLY_PROP_TIME_TO_FULL_AVG
- POWER_SUPPLY_PROP_TIME_TO_EMPTY_AVG

Calculations used are made for GEN3 FG based on the hardware
recommendation. Currently, TTF/TTE is only supported for normal
charging and Qnovo charging.

Change-Id: Icf08be89c674d682314230652c0202bba37db1cf
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>