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/Kconfig b/drivers/mfd/Kconfig
index 0f09c05..6ca938a 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -728,6 +728,9 @@
 	  if you say yes here you get support for the TPS65910 series of
 	  Power Management chips.
 
+config TPS65911_COMPARATOR
+	tristate
+
 endif # MFD_SUPPORT
 
 menu "Multimedia Capabilities Port drivers"