arm64: dts: m3ulcb: Update memory node to 2 GiB map

This patch updates memory region:

  - After changes, the new map of the m3ulcb board on R8A7796 SoC
    Bank0: 1GiB RAM : 0x000048000000 -> 0x0007fffffff
    Bank1: 1GiB RAM : 0x000600000000 -> 0x0063fffffff

  - Before changes, the old map looked like this:
    Bank0: 1GiB RAM : 0x000048000000 -> 0x0007fffffff

Signed-off-by: Vladimir Barinov <vladimir.barinov+renesas@cogentembedded.com>
Tested-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>