mm: Don't build mm_dump_obj() on CONFIG_PRINTK=n kernels

The mem_dump_obj() functionality adds a few hundred bytes, which is a
small price to pay.  Except on kernels built with CONFIG_PRINTK=n, in
which mem_dump_obj() messages will be suppressed.  This commit therefore
makes mem_dump_obj() be a static inline empty function on kernels built
with CONFIG_PRINTK=n and excludes all of its support functions as well.
This avoids kernel bloat on systems that cannot use mem_dump_obj().

Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: <linux-mm@kvack.org>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>