drm_hwcomposer: Simplify DrmAtomicStateManager thread usage

1. Remove PresentTracker class.
2. Use separate mutex for thread synchronization. Before, we have always
   experienced rescheduling due to calling condvar::notify inside the
   mutex, which consumes some number of CPU cycles.

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
diff --git a/hwc2_device/HwcDisplay.h b/hwc2_device/HwcDisplay.h
index 68353e9..4ad57b7 100644
--- a/hwc2_device/HwcDisplay.h
+++ b/hwc2_device/HwcDisplay.h
@@ -20,6 +20,7 @@
 
 #include <atomic>
 #include <optional>
+#include <sstream>
 
 #include "HwcDisplayConfigs.h"
 #include "compositor/LayerData.h"