libexternal: Add support for SPD Information

- SPD: Source product description.
- Retrieve the product vendor and name from the system
  property and pass it to the hdmi driver.
- This will display some specific names for source such
  as instead of "Input 1" it might display "QCOM 8974" for
  example

Change-Id: I5440841b9e47110386c793045f3b30774522dcb6
diff --git a/libexternal/external.h b/libexternal/external.h
index ce8e5d7..d35490f 100644
--- a/libexternal/external.h
+++ b/libexternal/external.h
@@ -60,6 +60,7 @@
     int  teardownWFDDisplay();
 
 private:
+    void setSPDInfo(const char* node, const char* property);
     void readCEUnderscanInfo();
     bool readResolution();
     int  parseResolution(char* edidStr, int* edidModes);