MLK-25482: watchdog: imx2_wdt: clear WDOG_HW_RUNNING before suspend

MLK-25482: watchdog: imx2_wdt: clear WDOG_HW_RUNNING before suspend

For watchdog_ping_work is not freezable so that it maybe scheduled before
imx2_wdt_resume where watchdog clock is on, hence, kernel will hang in
imx2_wdt_ping with clock disabled, and then watchdog reset happen.
Prevent the above case by clearing WDOG_HW_RUNNING before suspend, and
restore it with ping in imx2_wdt_resume.

Signed-off-by: Robin Gong <yibin.gong@nxp.com>
Reviewed-by: Jacky Bai <ping.bai@nxp.com>