mm, oom: check LMK enabled for pagefault_out_of_memory()

Rely on LMK to reclaim memory and avoid OOM, when out of memory
condition is detected in a pagefault.

pagefault_out_of_memory() may be called due to commit d1b75390beb8 ("mm:
reduce the time spend by killed tasks in alloc path"), which bails out from
alloc_pages_slowpath() if the current task has been killed.

Change-Id: Icfdaa51d7cfb0dfe9a665bcff23357101b15f421
Signed-off-by: Prakash Gupta <guptap@codeaurora.org>
Signed-off-by: Chris Goldsworthy <cgoldswo@codeaurora.org>