Use Tremor IMDCT for WMA. Gives a ~20% speedup on ARM and coldfire. All my test...

Use Tremor IMDCT for WMA.  Gives a ~20% speedup on ARM and coldfire.  All my test samples gave equivilent or better accuracy (>>16 bit), but there may still be problems.  Code becomes somewhat less readable since the IMDCT has bits of Vorbis in it, but this is not a serious issue and the old ffmpeg transform remains in SVN if anyone wants it.  Also, WMA now passes Vorbis as the fastest transform codec on ARM, although MPC remains the fastest lossy codec overall.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@18084 a1c6a512-1295-4272-9138-f99709370657