ARM: dts: vf500: Remove the zero length reg property

All the vf500 based boards include the real memory size in their
dts files, so remove the zero length reg property.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>