power: qpnp-fg: Enable FULL_SOC based on charging status

Currently, FULL_SOC interrupt is enabled as a wakeup interrupt
always. In some circumstances, it fires randomly after the
charger is removed but the SOC remains high. This wakes up the
device. Hence, keep it enabled only when the device is charging
and keep it disabled during discharging.

CRs-Fixed: 1075428
Change-Id: I575ba72030c3c453aac1118bceebe64a0445d138
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>