Move granite speech docs to audio models

Author: alex-jw-brooks

docs/source/en/_toctree.yml

@@ -485,8 +485,6 @@
         title: GraniteMoe
       - local: model_doc/granitemoeshared
         title: GraniteMoeShared
-      - local: model_doc/granite_speech
-        title: GraniteSpeech
       - local: model_doc/granitevision
         title: GraniteVision
       - local: model_doc/helium
@@ -821,6 +819,8 @@
         title: EnCodec
       - local: model_doc/fastspeech2_conformer
         title: FastSpeech2Conformer
+      - local: model_doc/granite_speech
+        title: GraniteSpeech
       - local: model_doc/hubert
         title: Hubert
       - local: model_doc/mctct