arm: dts: fsl-ls1088a: move memory node into U-Boot specific file

arm: dts: fsl-ls1088a: move memory node into U-Boot specific file

The top-level "memory" node does not exist in the Linux
version of the fsl-ls1088a.dtsi file. Move it to the U-Boot
"tweak" file, so we can have an identical copy of
fsl-ls1088a.dtsi between the projects in the end.

Signed-off-by: Mathew McBride <matt@traverse.com.au>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Tested-by: Ioana Ciornei <ioana.ciornei@nxp.com> # on LS1088A-RDB