msm8974: added input mediator

Brain dumb simple 2 level input event chain.
For clients that want input events to appear in a
certain order e.g. cpu hotplugging should get it
before cpufreq so that input boost is on all online
cpus

This is used in load_stats and rq_stats hotplugging
governor and in smartmax cpu governor

This is completely optional and will not influence
"normal" input event handling

Change-Id: I3e3c28cffb640ec0f543eea7994a55bfa4182221
Merge "msm8974: added input mediator" into android-4.4