SF: add HWVsync state to dumpsys

Log debugging information about whether HWVsync callbacks
where enabled with HWC.

Bug: 201605862
Test: adb logcat -s SurfaceFlinger
Change-Id: Iaa13a92d37fcfea1328a6e91b17372c3737ffff6
diff --git a/services/surfaceflinger/DisplayHardware/Hal.h b/services/surfaceflinger/DisplayHardware/Hal.h
index bb2888e..02d0658 100644
--- a/services/surfaceflinger/DisplayHardware/Hal.h
+++ b/services/surfaceflinger/DisplayHardware/Hal.h
@@ -166,4 +166,15 @@
     }
 }
 
+inline std::string to_string(hardware::graphics::composer::hal::Vsync vsync) {
+    switch (vsync) {
+        case hardware::graphics::composer::hal::Vsync::ENABLE:
+            return "Enable";
+        case hardware::graphics::composer::hal::Vsync::DISABLE:
+            return "Disable";
+        default:
+            return "Unknown";
+    }
+}
+
 } // namespace android