arm64: dts: ls1046a: add a dummy memory 'reg' property

The memory node in fsl-ls1046a.dtsi has no 'reg' property, and causes
the dtc warning below.

Warning (unit_address_vs_reg): Node /memory@80000000 has a unit name, but no reg property

Let's add a 'reg' property with dummy memory size, since bootloader will
need to fill the correct one per board memory configuration anyway.

Cc: Mingkai Hu <Mingkai.Hu@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Acked-by: Li Yang <leoyang.li@nxp.com>