libstagefright: Adds some parsing capability

o Adds AC3, EAC3 and DTS mime types
o Adds AC3/EAC3 support in MP4 parser
o Adds MPEG4 video, MPEG Audio, AC3, DTS, EAC3 support
in mkv extractor.

Change-Id: I9895c0e40e5ad38976004a9569200f1340d525de