mfd: AB3550 core driver

This adds a core driver for the AB3550 mixed-signal circuit
found in the ST-Ericsson U300 platforms. This driver
is a singleton proxy for all access to the AB3550 sub
functionality drivers which can be added on top of this one:
RTC, regulators, battery and system power control, vibrator,
LEDs and an ALSA codec.

Signed-off-by: Mattias Wallin <mattias.wallin@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 1c3d737..a20fa23 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -423,6 +423,20 @@
 	  read/write functions for the devices to get access to this chip.
 	  This chip embeds various other multimedia funtionalities as well.
 
+config AB3550_CORE
+        bool "ST-Ericsson AB3550 Mixed Signal Circuit core functions"
+	select MFD_CORE
+	depends on I2C=y && GENERIC_HARDIRQS && ABX500_CORE
+	help
+	  Select this to enable the AB3550 Mixed Signal IC core
+	  functionality. This connects to a AB3550 on the I2C bus
+	  and expose a number of symbols needed for dependent devices
+	  to read and write registers and subscribe to events from
+	  this multi-functional IC. This is needed to use other features
+	  of the AB3550 such as battery-backed RTC, charging control,
+	  LEDs, vibrator, system power and temperature, power management
+	  and ALSA sound.
+
 config MFD_TIMBERDALE
 	tristate "Support for the Timberdale FPGA"
 	select MFD_CORE