[GStreamer][Quirks][RPi] update additional playbin flags

https://bugs.webkit.org/show_bug.cgi?id=286668

Reviewed by Philippe Normand.

Set proper flags used by OpenMax.

* Source/WebCore/platform/gstreamer/GStreamerQuirkOpenMAX.h:

Canonical link: https://commits.webkit.org/289549@main

Author: pgorszkowski-igalia

Source/WebCore/platform/gstreamer/GStreamerQuirkOpenMAX.h

@@ -30,6 +30,7 @@ class GStreamerQuirkOpenMAX final : public GStreamerQuirk {
 public:
     GStreamerQuirkOpenMAX();
     const ASCIILiteral identifier() const final { return "OpenMAX"_s; }
+    unsigned getAdditionalPlaybinFlags() const final { return getGstPlayFlag("text") | getGstPlayFlag("native-video"); }
 
     bool processWebAudioSilentBuffer(GstBuffer*) const final;
 };