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>

include/linux/cache.h

@@ -60,4 +60,8 @@
 #endif
 #endif
 
+#ifndef CONFIG_ARCH_HAS_CACHE_LINE_SIZE
+#define cache_line_size()	L1_CACHE_BYTES
+#endif
+
 #endif /* __LINUX_CACHE_H */