arm64: dts: Add L2 cache topology to Hi6220

This patch adds the L2 cache topology on Hi6220. Hi6220 has two
clusters, every cluster has 512KiB L2 cache (32KiB x 16 ways).

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>