SF: Do not toggle idle timer on display hotplug

As a short-term measure to avoid a deadlock during display hotplug, skip
stopping and starting the pacesetter's idle timer on demotion/promotion.
This assumes that hotplug results in demoting/promoting the same display
as pacesetter, currently always the active internal display.

Fixes: 329450361
Flag: com.android.graphics.surfaceflinger.flags.connected_display
Test: Manual (foldable, connected display)
Change-Id: Ieeb026666c8abdd14e0d4690a624fb60306b1bc1