watchdog: omap_wdt: pet, do not disable, WDT at shutdown

Use WDT to recover from driver shutdown sequences that hang.

Change-Id: Ib794ea8ff7aa8f6f4b7e354f118b0d8f8eb98ddc
Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>