lmkd: Implement kill timeout

(cherry pick from commit caa2dc56)

New ro.lmk.kill_timeout_ms property defines timeout in ms after a
successful kill cycle for more kills to be considered. This is
necessary because memory pressure after a kill does not go down
instantly and system needs time to reflect new memory state. This
timeout prevents extra kills in the period immediately after a
kill cycle. By default it is set to 0 which disables this feature.

Bug: 63631020
Test: alloc-stress

Change-Id: Ia847118c8c4a659a7fc38cd5cd0042acb514ae28
Merged-In: Ia847118c8c4a659a7fc38cd5cd0042acb514ae28
Signed-off-by: Suren Baghdasaryan <surenb@google.com>