mfd: Add HI6421 PMIC Core driver

This adds driver to support HiSilicon Hi6421 PMIC. Hi6421 includes multi-
functions, such as regulators, codec, ADCs, Coulomb counter, etc.
This driver includes core APIs _only_.

Drivers for individul components, like voltage regulators, are
implemented in corresponding driver directories and files.

Registers in Hi6421 are memory mapped, so using regmap-mmio API.

Signed-off-by: Guodong Xu <guodong.xu@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
index bd11121..1d11a24 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -172,6 +172,7 @@
 obj-$(CONFIG_MFD_STW481X)	+= stw481x.o
 obj-$(CONFIG_MFD_IPAQ_MICRO)	+= ipaq-micro.o
 obj-$(CONFIG_MFD_MENF21BMC)	+= menf21bmc.o
+obj-$(CONFIG_MFD_HI6421_PMIC)	+= hi6421-pmic-core.o
 
 intel-soc-pmic-objs		:= intel_soc_pmic_core.o intel_soc_pmic_crc.o
 obj-$(CONFIG_INTEL_SOC_PMIC)	+= intel-soc-pmic.o