arm64: defconfig: enable support hi6421v530 PMIC

Enable configs for hi6421v530 mfd and regulator driver
 + CONFIG_MFD_HI6421_PMIC=y
 + CONFIG_REGULATOR_HI6421V530=y

Signed-off-by: Guodong Xu <guodong.xu@linaro.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>