mm: move cache_line_size() to <linux/cache.h>

Not all architectures define cache_line_size() so as suggested by Andrew move
the private implementations in mm/slab.c and mm/slob.c to <linux/cache.h>.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Reviewed-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slub.c

@@ -207,11 +207,6 @@ static inline void ClearSlabDebug(struct page *page)
 #define __KMALLOC_CACHE		0x20000000 /* objects freed using kfree */
 #define __PAGE_ALLOC_FALLBACK	0x10000000 /* Allow fallback to page alloc */
 
-/* Not all arches define cache_line_size */
-#ifndef cache_line_size
-#define cache_line_size()	L1_CACHE_BYTES
-#endif
-
 static int kmem_size = sizeof(struct kmem_cache);
 
 #ifdef CONFIG_SMP