SF: cleanup FlagManager

We currently use FlagManager just for boolean flags.
Remove the templated functions in favot of simpler ones.
Add macros for code reuse.

Test: presubmit
Change-Id: Iba892d981960b653466f55a52ed74a16138da75c
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index a36def7..3050520 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -689,6 +689,7 @@
         return;
     }
     mBootFinished = true;
+    FlagManager::getMutableInstance().markBootCompleted();
     if (mStartPropertySetThread->join() != NO_ERROR) {
         ALOGE("Join StartPropertySetThread failed!");
     }