ARM: config: enable ARCH_HIX5HD2

Since both ARCH_HI3xxx and ARCH_HIX5HD2 are based on Cortex A9 & they're
using similiar kernel features, make them share the hi3xxx_config.

And add it into multi_v7_defconfig too.

Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>
Acked-by: Wei Xu <xuwei5@hisilicon.com>
[olof: also turn on ARCH_HISI in multi_v7]
Signed-off-by: Olof Johansson <olof@lixom.net>