hwc2: Add support to query display wb capabilities

Virtual display uses hardware wb to get output data.
And output buffer format depends on wb hardware capabilities.

Change-Id: If06b9e36eeda630938b07933878fe2d148ea9bcb
diff --git a/libdisplayconfig/DisplayConfig.h b/libdisplayconfig/DisplayConfig.h
index 17b6421..fbce8b6 100644
--- a/libdisplayconfig/DisplayConfig.h
+++ b/libdisplayconfig/DisplayConfig.h
@@ -83,6 +83,10 @@
     float min_luminance = 0.0f;
 };
 
+struct WriteBackCapabilities {
+    bool isWbUbwcSupported;
+};
+
 //=============================================================================
 // The functions below run in the client pocess and wherever necessary
 // do a binder call to HWC to get/set data.
@@ -104,6 +108,7 @@
 int getHDRCapabilities(int dpy, DisplayHDRCapabilities *caps);
 int setCameraLaunchStatus(uint32_t on);
 bool displayBWTransactionPending();
+int32_t getWriteBackCapabilities( WriteBackCapabilities *caps);
 
 } // namespace display