mfd: Factor out WM831x I2C I/O from the core driver

In preparation for the addition of SPI support for the WM831x move the I2C
specific code into a separate file with a separate Kconfig option so the
I2C support can be excluded from the build.

Also update the 1133-EV1 PMIC module support for SMDK6410 to use the new
symbol.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 6c6b9f0..2fb1e89 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -315,14 +315,19 @@
 	  the functionality of the device.
 
 config MFD_WM831X
-	bool "Support Wolfson Microelectronics WM831x/2x PMICs"
+	bool
+	depends on GENERIC_HARDIRQS
+
+config MFD_WM831X_I2C
+	bool "Support Wolfson Microelectronics WM831x/2x PMICs with I2C"
 	select MFD_CORE
+	select MFD_WM831X
 	depends on I2C=y && GENERIC_HARDIRQS
 	help
-	  Support for the Wolfson Microelecronics WM831x and WM832x PMICs.
-	  This driver provides common support for accessing the device,
-	  additional drivers must be enabled in order to use the
-	  functionality of the device.
+	  Support for the Wolfson Microelecronics WM831x and WM832x PMICs
+	  when controlled using I2C.  This driver provides common support
+	  for accessing the device, additional drivers must be enabled in
+	  order to use the functionality of the device.
 
 config MFD_WM8350
 	bool