SF: Read PRESENT_FENCE_IS_NOT_RELIABLE once

Avoid per-frame (hash) lookups and off-main-thread locking.

Bug: 324366212
Test: presubmit
Change-Id: Ia34bbfe9e6be6f87fac63738a71c62d34a6599db
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index be05797..8fc819d 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -1221,6 +1221,7 @@
     // constant members (no synchronization needed for access)
     const nsecs_t mBootTime = systemTime();
     bool mIsUserBuild = true;
+    bool mHasReliablePresentFences = false;
 
     // Can only accessed from the main thread, these members
     // don't need synchronization