power: smb5-lib: unify wdog timer for SW step-charging

Currently, SW Step charging is periodically evaluated on different wdog
timers, with some targets on bark for every 16s and others on snarl for
8s.

However, recent charger SW optimization for wakeups requires 8s timeout,
which is for all targets.

Update with snarl 8s timer for all.

Change-Id: Ie29d836298b8a9b799ee082386c3051c70e1ff6d
Signed-off-by: Harry Yang <harryy@codeaurora.org>