Define constants in IStreamListener in MediaKeys.h

Currently, constants in IStreamSource are being used in ATSParser while
they are separate entities. This defines those constants in MediaKeys.h
so that ATSParser can be used without depending on IStreamSource.

This removes libmedia dependency from libmpeg2extractor.

Test: build.
Bug: 67908537
Change-Id: I503a4cdb530825b1932463efae999d120b839e56