Allow lmkd write access to sys.lmk. properties to be able to set
sys.lmk.minfree_levels.

Bug: 111521182
Test: getprop sys.lmk.minfree_levels returns value set by lmkd
Change-Id: I86ff11d75917966857d3a76876a56799bb92a5ad
Signed-off-by: Suren Baghdasaryan <surenb@google.com>