backport lowmemorykiller from CAF msm-3.4

this improves low memory behaviour greatly due to accounting for
lowmem_reserve as well as shmem pages.

Change-Id: I351dda49be388a98edfe6cc31ae4f2667c77429c
(cherry picked from commit a64a14050e32fa79905903cf76c62be5b360c8eb)