mm: oom-kill: Add lmk_kill possible for ULMK

While ULMK is active, prevent OOM for order <= COSTLY_ORDER
pages. No special actions are taken for larger orders.

Change-Id: I4ccba1b71155947569acc3d88ae2027e3b2e0620
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>
Signed-off-by: Chris Goldsworthy <cgoldswo@codeaurora.org>