Add the lowmem module

lowmem is an LSM module for notifying user space about
low memory situations, and for tweaking the vm_enough_memory()
implementation to be better suited for embedded devices.

Signed-off-by: Juha Yrjola <juha.yrjola@solidboot.com>

diff --cc security/Kconfig
Simple merge

diff --cc security/Makefile
Simple merge

diff --cc security/lowmem.c
Simple merge