mfd: Add ST Multi-Function eXpander (STMFX) core driver

STMicroelectronics Multi-Function eXpander (STMFX) is a slave controller
using I2C for communication with the main MCU. Main features are:
- 16 fast GPIOs individually configurable in input/output
- 8 alternate GPIOs individually configurable in input/output when other
STMFX functions are not used
- Main MCU IDD measurement
- Resistive touchscreen controller

Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/Kconfig

@@ -1907,6 +1907,19 @@ config MFD_STPMIC1
 	  To compile this driver as a module, choose M here: the
 	  module will be called stpmic1.
 
+config MFD_STMFX
+	tristate "Support for STMicroelectronics Multi-Function eXpander (STMFX)"
+	depends on I2C
+	depends on OF || COMPILE_TEST
+	select MFD_CORE
+	select REGMAP_I2C
+	help
+	  Support for the STMicroelectronics Multi-Function eXpander.
+
+	  This driver provides common support for accessing the device,
+	  additional drivers must be enabled in order to use the functionality
+	  of the device.
+
 menu "Multimedia Capabilities Port drivers"
 	depends on ARCH_SA1100
 

drivers/mfd/Makefile

@@ -246,4 +246,4 @@ obj-$(CONFIG_MFD_MXS_LRADC)     += mxs-lradc.o
 obj-$(CONFIG_MFD_SC27XX_PMIC)	+= sprd-sc27xx-spi.o
 obj-$(CONFIG_RAVE_SP_CORE)	+= rave-sp.o
 obj-$(CONFIG_MFD_ROHM_BD718XX)	+= rohm-bd718x7.o
-
+obj-$(CONFIG_MFD_STMFX) 	+= stmfx.o