cmds/stagefright: use MediaCodec* instead of OMXCodec

OneShotDecodingSource is a lightweight replacement for OMXCodec
for decoding use. It does not support pause, secure content or
precise seeking.

'stagefright' now lists the codec profiles for all OMX codecs,
not just the regular ones.

Change-Id: I99f0f79af852a8a16607218acd9fdd83457b7f70
(cherry picked from commit bf03e42c)