arm64: dts: renesas: v3msk: Fix memory size

The V3MSK board has 2 GiB RAM according to the datasheet and schematics.

Signed-off-by: Valentine Barshak <valentine.barshak@cogentembedded.com>
[geert: Verified schematics]
Fixes: cc3e267e ("arm64: dts: renesas: initial V3MSK board device tree")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20210326121050.1578460-1-geert+renesas@glider.be