Go: Add defaults for downgrade_pressure and kill_heaviest_task

Explicitly define ro.lmk.downgrade_pressure and ro.lmk.kill_heaviest_task
values for Go so that defaults can be safely changed if needed.

Change-Id: I86d9c7aa52c213c43a25b02844e054dc28a6e512
Signed-off-by: Suren Baghdasaryan <surenb@google.com>