arm64: dts: Add dts files for Hisilicon Hi6220 SoC

Add initial dtsi file to support Hisilicon Hi6220 SoC with
support of Octal core CPUs in two clusters and each cluster
has quard Cortex-A53.

Also add dts file to support HiKey development board which
based on Hi6220 SoC.

Signed-off-by: Bintian Wang <bintian.wang@huawei.com>
Acked-by: Haojian Zhuang <haojian.zhuang@linaro.org>
Reviewed-by: Yiping Xu <xuyiping@hisilicon.com>
Tested-by: Will Deacon <will.deacon@arm.com>
Tested-by: Tyler Baker <tyler.baker@linaro.org>
Tested-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>