rework cuesheet support:
swcodec: search for a .cue during buffering (with the possibility of adding embedded cuesheets later)
hwcodec: search for a .cue when the id3 info for the current track is requested for the first time (disk should be spining so non issue)
major beenfit from this is simplofy cuesheet handling code a bit... if mp3entry.cuesheet != NULL then there is a valid cuesheet.. no need to worry about if its enabled and preloaded.
There is the possibility of putting the next/prev subtrack handling inside the playback code (as well as the id3 updating stuff (see FS#9789 for more info), but thats probably not a good idea.
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@21978 a1c6a512-1295-4272-9138-f99709370657