arm: socfpga: Add watchdog disable for socfpga

This adds watchdog disable. It is neccessary for running Linux kernel.

Signed-off-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <clsee@altera.com>
Cc: Dinh Nguyen <dinguyen@altera.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Tom Rini <trini@ti.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Pavel Machek <pavel@denx.de>

V2: Move RSTMGR_PERMODRST_L4WD0_LSB to reset_manager.h
    Reset watchdog only if CONFIG_HW_WATCHDOG is undefined (the default)