SystemUI: nav bar menu keys as left and right dpad arrows

ps3: null check
ps4/5: more consistent implementation
	now properly hides on lockscreen if keyboard is
	still up. the arrow keys should also work with any
	navigation bar configuration that we support right
	now

Change-Id: Iba75e8f1b19f299a1b7ff607c33679d9788cd925
Signed-off-by: Roman Birg <romanbirg@gmail.com>