ARM: dts: imx51-zii-scu2-mezz: Disable VPU

imx51-zii-scu2-mezz does not have any video encoding/decoding needs,
so disable the VPU.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Acked-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>