hwc: Set default idle timeout to 70ms

Set default idle timeout to 70ms (~4 cycles on 60fps panel + some extra)
from the earlier 2sec.
The GPU timeout is around 80ms after which it turns off its rail,
clock and bus vote. So having a draw cycle before that is beneficial

Change-Id: I03291a4b8fd0707839567987febe1c088e21c92d
1 file changed