ARM: hisi: rename hi3xxx to hisi

Since some new Hisilicon SoCs are not named as hi3xxx, rename mach-hi3xxx
to mach-hisi instead. And the pronounciation of "hisi" is similar to the
chinese pronounciation of Hisilicon. So Hisilicon guys like this name.

ARCH_HI3xxx will be renamed later since other drivers are using it and
they are still in linux-next git tree. So rename ARCH_HI3xxx later.

Signed-off-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Kevin Hilman <khilman@linaro.org>