libexternal: Add support for changing resolution on HDMI

- set the property hdmi.resolution with the required mode
  (16,4,3,32,34,1)
- If that resolution is not supported by the TV, it will fall
  back to the best mode supported by the TV

Change-Id: I90ceda02319e79e388035ba7b5926bdcf6625595
CRs-fixed: 430055
diff --git a/libexternal/external.h b/libexternal/external.h
index 46c982d..d85ce44 100644
--- a/libexternal/external.h
+++ b/libexternal/external.h
@@ -55,7 +55,9 @@
     bool isValidMode(int ID);
     void handleUEvent(char* str, int len);
     int  getModeOrder(int mode);
+    int  getUserMode();
     int  getBestMode();
+    bool isInterlacedMode(int mode);
     void resetInfo();
     void setDpyHdmiAttr();
     void setDpyWfdAttr();