Unify handling of DRM devices between DRM and VAAPI

SDL may not be able to give us a DRM FD for Vulkan windows.

app/streaming/video/ffmpeg-renderers/drm.h

@@ -86,6 +86,7 @@ private:
     AVHWDeviceType m_HwDeviceType;
     AVBufferRef* m_HwContext;
     int m_DrmFd;
+    bool m_DrmIsMaster;
     bool m_SdlOwnsDrmFd;
     bool m_SupportsDirectRendering;
     int m_VideoFormat;