ARM: dts: exynos: add CPU topology to Exynos3250

Describe Exynos3250 CPU topology.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210731092409.31496-1-krzysztof.kozlowski@canonical.com