debugobjects: Track number of kmem_cache_alloc/kmem_cache_free done

New debugfs stat counters are added to track the numbers of
kmem_cache_alloc() and kmem_cache_free() function calls to get a
sense of how the internal debug objects cache management is performing.

Signed-off-by: Waiman Long <longman@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: "Du Changbin" <changbin.du@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jan Stancek <jstancek@redhat.com>
Link: http://lkml.kernel.org/r/1483647425-4135-2-git-send-email-longman@redhat.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>