arm: socfpga: Use DM watchdog timer

All SoCFPGA platforms (except Cyclone V) are now switching
to CONFIG_WDT (driver model for watchdog timer drivers)
from CONFIG_HW_WATCHDOG.

Signed-off-by: Chee Hong Ang <chee.hong.ang@intel.com>
Reviewed-by: Ley Foon Tan <ley.foon.tan@intel.com>
7 files changed