BACKPORT: mm/zpool: zbud/zsmalloc implement zpool

(cherry-pick from commit c795779df29e180738568d2a5eb3a42f3b5e47f0)

Update zbud and zsmalloc to implement the zpool api.

Bug: 25951511

Change-Id: Ib58729c1efeb4834d566d29f9abf33fec1f7f79d
[fengguang.wu@intel.com: make functions static]
Signed-off-by: Dan Streetman <ddstreet@ieee.org>
Tested-by: Seth Jennings <sjennings@variantweb.net>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Weijie Yang <weijie.yang@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>