stagefright: Fix codec lookup bugs on NuPlayer

 * Fix use of WMA/WMV software codecs
 * Fix mpeg2 software codec name
 * Don't override the component name in ACodec. This actually breaks
   stuff because the format isn't available in the kInit message.

Change-Id: I93c292e039de5f24c2ccbd6ae2242b06d28fe518