Various cleanups in code surrounding the state semaphore:
- inline spu_acquire/spu_release
- cleanup spu_acquire_* and add kerneldoc comments to these functions
- remove spu_release_exclusive and replace it with spu_release
Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>