mfd: Add WM831x SPI support

Implement support for controlling WM831x and WM832x devices using SPI.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
index c9ef41b..f54b365 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -25,6 +25,7 @@
 wm831x-objs			:= wm831x-core.o wm831x-irq.o wm831x-otp.o
 obj-$(CONFIG_MFD_WM831X)	+= wm831x.o
 obj-$(CONFIG_MFD_WM831X_I2C)	+= wm831x-i2c.o
+obj-$(CONFIG_MFD_WM831X_SPI)	+= wm831x-spi.o
 wm8350-objs			:= wm8350-core.o wm8350-regmap.o wm8350-gpio.o
 wm8350-objs			+= wm8350-irq.o
 obj-$(CONFIG_MFD_WM8350)	+= wm8350.o