socfpga: Adding DesignWare watchdog support

To enable the DesignWare watchdog support at SOCFPGA
Cyclone V dev kit.

Signed-off-by: Chin Liang See <clsee@altera.com>
Cc: Anatolij Gustschin <agust@denx.de>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Heiko Schocher <hs@denx.de>
Cc: Tom Rini <trini@ti.com>