decklink: Add option to select pixel format

This replaces the name-based detection of the 4K intensity pro, and
allows other devices to be able to use the BGRA pixel format, if the
user so chooses.

plugins/decklink/decklink-device-instance.hpp

@@ -28,6 +28,8 @@ public:
 		return mode ? mode->GetId() : 0;
 	}
 
+	inline BMDPixelFormat GetActivePixelFormat() const {return pixelFormat;}
+
 	inline DeckLinkDeviceMode *GetMode() const {return mode;}
 
 	bool StartCapture(DeckLinkDeviceMode *mode);