soc: wdog: Ensure missing user watchdog pet can trigger bite

The user watchdog was waiting the hardware watchdog bite by
stop petting it. But in the cpu suspend scenarios, the auto petting
by hardware prevent the expected watchdog bite. So add a new user pet
timer to explicitly trigger the watchdog bite by software when the user
watchdog petting is not happenned before timeout.

Change-Id: I71b1139192baa960ae00f7a27c630aedaf5a3ffa
Signed-off-by: Maria Yu <aiquny@codeaurora.org>