arm64: dts: mt8192: Fix CPU map for single-cluster SoC

MT8192 features the ARM DynamIQ technology and combines both four
Cortex-A76 (big) and four Cortex-A55 (LITTLE) CPUs in one cluster:
fix the CPU map to reflect that.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Fixes: 48489980 ("arm64: dts: Add Mediatek SoC MT8192 and evaluation board dts and Makefile")
Link: https://lore.kernel.org/r/20230126103526.417039-3-angelogioacchino.delregno@collabora.com


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