ARM: hisi: enable hix5hd2 SoC

Enable support for the Hisilicon HiX5HD2 SoC. This HiX5HD2 SoC series
support both single and dual Cortex-A9 cores.

Add ARCH_HIX5HD2 to distinguish HiX5HD2 from Hi3xxx.

They are different in implementation such as SMP, IPs integarted and
earlycon configure.

Signed-off-by: Haifeng Yan <yanhaifeng@gmail.com>
Signed-off-by: Jiancheng Xue <jchxue@gmail.com>
Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>
Acked-by: Wei Xu <xuwei5@hisilicon.com>
Signed-off-by: Olof Johansson <olof@lixom.net>