ARM: dts: vf610-zii-ssmb-spu3: Disable watchdog

On vf610-zii-ssmb-spu3 board there is a supervisory microcontroller that
provides the watchdog functionality, so disable the on-chip Vybrid's
watchdog.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>