SF: Fix jank after folding due to power sequence

SF assumed that DM always powers off the active display before powering
on the other display. However, this is not the case when simultaneously
folding and pressing the power button to turn on the rear display.

SF then behaves as if all displays were off (e.g. synthetic VSYNC, low
thread priority), causing consistent jank until the next power or fold
event. Fix this by activating the other display if already powered on.

Fixes: 294230902
Test: No jank after simultaneously folding and hitting the power button.
Test: FoldableTest.promotesPacesetterOnConcurrentPowerOff
Change-Id: I5d0bdafc4002ce5ae86866f457132f8a0f178698