SF: Extend synthetic vsync and thread optimizations to external displays

Synthetic vsync and thread scheduling optimizations are currently gated
for internal displays only. This CL removes the limitation such that
they are applicable to external displays.

Flag: com.android.graphics.surfaceflinger.flags.pacesetter_selection
Bug: 380251940
Test: SetPhysicalDisplayPowerModeTest (ExternalDisplayPowerCase)
Change-Id: I7e33c132c165b29a24194c98a699a6ce83d01562