mfd: Use AB3100 MFD core IRQ for interrupt randomness

This reintroduces the entropy sampling of the AB3100 IRQ as the
IRQF_SAMPLE_RANDOM is going out according to the feature removal
schedule. I'm trying to do this the right way then, so CC:ing some
random people for a quick review. We add entropy for interrupt
events in the AB3100 which are truly random in nature, like
external cables being connected, voltages on batteries dropping
below certain ranges, ADC triggers or overheating.

Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Cc: Robin Getz <rgetz@blackfin.uclinux.org>
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 9bcd447..ea2557b 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -329,8 +329,8 @@
 	 the PCF50633 chip.
 
 config AB3100_CORE
-	tristate "ST-Ericsson AB3100 Mixed Signal Circuit core functions"
-	depends on I2C
+	bool "ST-Ericsson AB3100 Mixed Signal Circuit core functions"
+	depends on I2C=y
 	default y if ARCH_U300
 	help
 	  Select this to enable the AB3100 Mixed Signal IC core