ARM: dts: imx: Remove empty memory size nodes

Remove the empty reg property from the SoC dtsi files in order to avoid
duplicate memory nodes when the correct size is passed in board dts files.

Signed-off-by: Marco Franchi <marco.franchi@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>