imx8m: Enable WDOG_B for timeout

imx8m: Enable WDOG_B for timeout

When doing reset_cpu, in normal case the WDOG_B outputs immediately
after we clean WDA bit. But on mscale, the WDOG_B may be later than
internal reset, and cause PMIC not reset. As we enabled the SD3.0
support, the PMIC must be reset to reset SD card.

Change the reset_cpu to enable the WDOG_B for timeout as well, and set
WDOG timeout to 1s.

Reviewed-by: Fabio Estevam <festevam@gmail.com>
Acked-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>