hwc: Add some debug and warning logs.

Add debug logs for blank, unblank and warning logs for composition on powerdown.

Change-Id: I184a9503a26d401cf70e072815603a47d3972eed
diff --git a/libhwcomposer/hwc_utils.h b/libhwcomposer/hwc_utils.h
index 04bf864..9cb6e15 100644
--- a/libhwcomposer/hwc_utils.h
+++ b/libhwcomposer/hwc_utils.h
@@ -156,6 +156,7 @@
 
     qhwc::MDPInfo mMDP;
 
+    bool isPoweredDown;
 };
 
 #endif //HWC_UTILS_H