- splitted pcm channels in two different devices to handle mmap correctly

- splitted pcm channels in two different devices to handle mmap correctly
- removed mmap control device
- reordered pcm shared and not shared code
- changed O_WRONLY oss pcm modifier in a more symmetric and elegant way
- changed slightly control interface
- added snd-debug-check
- uniformed null pointer check
- fixed a typo in linear plugin