binfmt_elf.c: use get_random_int() to fix entropy depleting.

Usually the entropy pool depletes very fast and stays in the 100-200 range.
After this patch, the entropy stays in the 600-1000 range without the risk of
depleting in normal workloads.

Change-Id: Ice0d0f14691046249d7b4a4d31af98ab80c6306b
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)
lowmemorykiller: skip already freed memory

Change-Id: I1cb221ff7dad399b3b57817706812561f67c6707