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>