mfd: Add Makefile and Kconfig Entries for tps65911 comparator

Base on Mark's comment [1], I make the Kconfig entry invisible to users.
[1] https://lkml.org/lkml/2011/5/14/136

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
index efe3cc3..d7d47d2 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -94,3 +94,4 @@
 obj-$(CONFIG_MFD_PM8921_CORE) 	+= pm8921-core.o
 obj-$(CONFIG_MFD_PM8XXX_IRQ) 	+= pm8xxx-irq.o
 obj-$(CONFIG_MFD_TPS65910)	+= tps65910.o tps65910-irq.o
+obj-$(CONFIG_TPS65911_COMPARATOR)	+= tps65911-comparator.o