mm: move slab related stuff from util.c to slab_common.c

Functions krealloc(), __krealloc(), kzfree() belongs to slab API, so
should be placed in slab_common.c

Also move slab allocator's tracepoints defenitions to slab_common.c No
functional changes here.

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>