hwc: Perform MDP downscaling for WFD/HDMI Scenario

  On WFD/HDMI connection, if the configured resolution is less than
  Primary Resolution, Display HAL does the following:

  1. sends hpd notification to SF with primary resolution.
  2. configures MDP pipes with configured Resolution.

  This is done to improve UI quality as MDP has better downscale
  filter options compared to GPU.
  This works only for QCOM WFD proprietary solution.

Change-Id: Ic20e837bf02c0f7b6718946e70b936f3a469fa7c
diff --git a/libexternal/external.h b/libexternal/external.h
index 2fbb027..1a3602d 100644
--- a/libexternal/external.h
+++ b/libexternal/external.h
@@ -45,6 +45,7 @@
     void setActionSafeDimension(int w, int h);
     bool isCEUnderscanSupported() { return mUnderscanSupported; }
     int configure();
+    void getAttributes(int& width, int& height);
     int teardown();
     bool isConnected() {
         return  mHwcContext->dpyAttr[HWC_DISPLAY_EXTERNAL].connected;