qpnp-fg-gen3: update empty voltage threshold and empty SOC irq handling

As per the hardware characterization, update the battery empty
voltage threshold to 2.8V. Since this moves the voltage little
away from cutoff voltage, update the empty SOC interrupt handling
to report SOC as 0. Since we only need the rising edge of empty
SOC interrupt, modify the interrupt flag as well.

Change-Id: I665a6f879af4e6b6e9f94b5464be7894d5ea67cb
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>