mfd: Add AAT2870 mfd driver

Add mfd core driver for AnalogicTech AAT2870.
The AAT2870 is communication through I2C and contains backlight and
regulator components.

Signed-off-by: Jin Park <jinyoungp@nvidia.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
index ca1867d..c580203 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -101,3 +101,4 @@
 obj-$(CONFIG_MFD_PM8921_CORE) 	+= pm8921-core.o
 obj-$(CONFIG_MFD_PM8XXX_IRQ) 	+= pm8xxx-irq.o
 obj-$(CONFIG_TPS65911_COMPARATOR)	+= tps65911-comparator.o
+obj-$(CONFIG_MFD_AAT2870_CORE)	+= aat2870-core.o