soc: qcom: watchdog_v2: use rt task to pet watchdog

As scheduler doesn't guarantee scheduling even into high
priority worker task within 1 sec after waking up, it can't
pet watchdog properly. Use rt task to pet watchdog even if
the scheduler is busy to handle normal priority tasks.

Change-Id: Ief8a01df8ef61481c94c3f781d22796882320fc0
Signed-off-by: Se Wang (Patrick) Oh <sewango@codeaurora.org>