mfd: Add support for the MediaTek MT6397 PMIC

This adds support for the MediaTek MT6397 PMIC. This is a
multifunction device with the following sub modules:

- Regulator
- RTC
- Audio codec
- GPIO
- Clock

It is interfaced to the host controller using SPI interface by a proprietary
hardware called PMIC wrapper or pwrap. MT6397 MFD is a child device of the
pwrap.

Signed-off-by: Flora Fu, MediaTek
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
index c8bb349..26303f7 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -181,3 +181,4 @@
 
 intel-soc-pmic-objs		:= intel_soc_pmic_core.o intel_soc_pmic_crc.o
 obj-$(CONFIG_INTEL_SOC_PMIC)	+= intel-soc-pmic.o
+obj-$(CONFIG_MFD_MT6397)	+= mt6397-core.o