stagefright: ExtendedStats: Only enable stats with property

Only enable the extendedstats when property:
persist.debug.sf.extendedstats is set to 1. Change the constructor
of AutoProfile to pass the MediaExtendedStats module and do the
NULL check inside it instead of at every call.

Change-Id: I0d41469e41f358506638d76dc995ed3acda2b403