mfd: hi6421-pmic: Add support for HiSilicon Hi6421v530

Add support for HiSilicon Hi6421v530 PMIC. Hi6421v530 communicates with
main SoC via memory-mapped I/O.

Hi6421v530 and Hi6421 are PMIC chips from the same vendor, HiSilicon,
but at different revisions. They share the same memory-mapped I/O
design. They differ in integrated devices, such as regulator details,
LDO voltage points.

Signed-off-by: Guodong Xu <guodong.xu@linaro.org>
Signed-off-by: Wang Xiaoyin <hw.wangxiaoyin@hisilicon.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>