intel/perf: create a vtable entry for emit_mi_flush

This method is needed to move subsequent methods into perf.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/intel/perf/gen_perf.h

@@ -217,6 +217,7 @@ struct gen_perf_config {
    struct {
       void *(*bo_alloc)(void *bufmgr, const char *name, uint64_t size);
       void (*bo_unreference)(void *bo);
+      void (*emit_mi_flush)(void *ctx);
       void (*emit_mi_report_perf_count)(void *ctx,
                                         void *bo,
                                         uint32_t offset_in_bytes,