Display options: allow configuration of wake on plug behavior (2/2)

The PowerManager now checks Settings.Global.WAKE_WHEN_PLUGGED_OR_UNPLUGGED
to determine wake-on-plug behavior.  The configuration option
config_unplugTurnsOnScreen is used as the default value of the setting.

PS 2: Fix formatting of if statement

Cherry-picked from: I062794828831a2b6faf4293579103d2251f1bdd0

Change-Id: I7eefff468a64c04e536c377cff3c740a7e568ade