UPSTREAM: tools/vm/slabinfo: Handle files in debugfs

Commit 64dd6849 relocated and renamed the alloc_calls and
free_calls files from /sys/kernel/slab/NAME/*_calls over to
/sys/kernel/debug/slab/NAME/*_calls but didn't update the slabinfo tool
with the new location.

This change will now have slabinfo look at the new location (and filenames)
with a fallback to the prior files.

Bug: 254441685
Fixes: 64dd6849 ("mm: slub: move sysfs slab alloc/free interfaces to debugfs")
Cc: stable@vger.kernel.org
Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Tested-by: Stéphane Graber <stgraber@ubuntu.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
(cherry picked from commit 0c7e0d69)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: Ibb4fb7c6159d5582455b97a671b4a53faa38829a