arm64: dts: mediatek: Increase the size BL31 reserved memory

The reserved size for BL31 is too small.
This has been highlighted by the MPU that now restrict access to BL31
memory to secure world only.
This increase the size of the reserved memory.

Signed-off-by: Alexandre Bailon <abailon@baylibre.com>
Signed-off-by: Alexandre Mergnat <amergnat@baylibre.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230203-evk-board-support-v3-3-0003e80e0095@baylibre.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>