ENGR00287983-2 imx restart: add another WDOG2 reset support for ldo-bypass

ENGR00287983-2 imx restart: add another WDOG2 reset support for ldo-bypass

For ldo-bypass mode on i.MX6Q/DL sabresd board, we will use another WDOG2 to
reset external pmic to trigger POR event, rather than WDOG1 to trigger WDOG
event in ldo-enable mode. We need to consider it in common mxc_restart().
On i.MX6SL sabresd board we use WDOG1 to trigger WDOG event both ldo-bypass and
ldo-enable mode.

Signed-off-by: Robin Gong <b38343@freescale.com>