tools/vm/slabinfo: update options in usage message

Currently usage message list only a subset of the available options.
should list them all.

Update options in usage massage to include all available options.

Link: http://lkml.kernel.org/r/20190212001219.27769-2-tobin@kernel.org
Signed-off-by: Tobin C. Harding <tobin@kernel.org>
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>