radv: flush VGT streamout like PAL
This fixes KHR-GL45.transform_feedback_overflow_query_ARB.multiple-streams-one-buffer-per-stream on zink/radv.
PAL uses the event write for some reason here.
This fixes KHR-GL45.transform_feedback_overflow_query_ARB.multiple-streams-one-buffer-per-stream on zink/radv.
PAL uses the event write for some reason here.