mm/slab: move SLUB alloc hooks to common mm/slab.h

mm/slab: move SLUB alloc hooks to common mm/slab.h

First step towards sharing alloc_hook's between SLUB and SLAB
allocators.  Move the SLUB allocators *_alloc_hook to the common
mm/slab.h for internal slab definitions.

Signed-off-by: Jesper Dangaard Brouer <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>