Make PCM->driver interface about as simple as it will get. Registered callback, zero...

Make PCM->driver interface about as simple as it will get. Registered callback, zero data, alignment and stops are handled entirely inside pcm.c; driver merely calls fixed pcm.c callback. Remove pcm_record_more and do it just like playback; the original reason behind it isn't very practical in general. Everything checks out on supported targets. There wer some compat changes I can't check out on many unsupoorted but if there's a problem it will be a minor oops. Plugins become incompatible due to recording tweak-- full update. Sorted API.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@26253 a1c6a512-1295-4272-9138-f99709370657