Use a separate class to manage virtio-gpu fence signaling

Use a separate class with queues to record the virtio-gpu fences and
their payloads, and call the callback of fences once all previous tasks
on the timeline is marked complted.

Test: run the emulator, VirtioGputTimelines_unittests

Change-Id: I57a2ce5cee1781a2a3b511a43e96b347208571cc
diff --git a/stream-servers/Android.bp b/stream-servers/Android.bp
index 18f4eea..8547650 100644
--- a/stream-servers/Android.bp
+++ b/stream-servers/Android.bp
@@ -81,6 +81,7 @@
         "GfxStreamAgents.cpp",
         "virtio-gpu-gfxstream-renderer.cpp",
         "GfxStreamBackend.cpp",
+        "VirtioGpuTimelines.cpp",
     ],
     host_ldlibs: [
         "-lpthread",