Fix screen not turning off correctly.

If a device was not set to doze after sleep, it was possible to hit the
power button and for the display to not turn off.

This change makes the display go to the off state if there is another
display which is currently on in this scenario.

Test: manual - Use device with external display. Hit power button.
Detach external display.
Bug: 185934103

Change-Id: I6412955ee44d13c4fbab4167f4f3a26415441983