mfd: Add WM8994 interrupt controller support

The WM8994 has an interrupt controller which supports interrupts for
both CODEC and GPIO portions of the chip. Support this using genirq,
while allowing for systems that do not have an interrupt hooked up.

Wrapper functions are provided for the IRQ request and free to simplify
the code in consumer drivers when handling cases where IRQs are not
set up.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index b2073e0..de3e74c 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -301,9 +301,9 @@
 	  selected to enable support for the functionality of the chip.
 
 config MFD_WM8994
-	tristate "Support Wolfson Microelectronics WM8994"
+	bool "Support Wolfson Microelectronics WM8994"
 	select MFD_CORE
-	depends on I2C
+	depends on I2C=y && GENERIC_HARDIRQS
 	help
 	  The WM8994 is a highly integrated hi-fi CODEC designed for
 	  smartphone applicatiosn.  As well as audio functionality it