rtph265pay: Define and use FU_A_TYPE_ID
rtph265pay: Define and use FU_A_TYPE_ID

Align with rtph264pay

pexip/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good