hwc: Allow HWC to support Virtual Display

  This change allows virtual display to be composed
  by HWC for supporting Google WFD App + QCOM WFD stack.

Change-Id: If8892230256e72fa34e3fb5ae715c3ad8cbd5b64
diff --git a/libexternal/external.h b/libexternal/external.h
index baf3598..39f8645 100644
--- a/libexternal/external.h
+++ b/libexternal/external.h
@@ -46,6 +46,7 @@
     bool isCEUnderscanSupported() { return mUnderscanSupported; }
     void setExternalDisplay(bool connected, int extFbNum = 0);
     bool isExternalConnected() { return mConnected;};
+    void  setExtDpyNum(int extDpyNum) { mExtDpyNum = extDpyNum;};
     bool post();
     void setHPD(uint32_t startEnd);
     void setEDIDMode(int resMode);
@@ -92,6 +93,7 @@
     fb_var_screeninfo mVInfo;
     int mHdmiFbNum;
     int mWfdFbNum;
+    int mExtDpyNum;
 };
 
 }; //qhwc