xa: don't leak fences

XA was never unref'ing last_fence in the various call paths to
pipe->flush().  Add this to xa_context_flush() and update the other
open-coded calls to pipe->flush() to use xa_context_flush() instead.

This fixes a memory leak reported with xf86-video-freedreno.

Reported-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Cc: "10.5 10.6" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Rob Clark <robclark@freedesktop.org>
(cherry picked from commit 0a8af6361e)

src/gallium/state_trackers/xa/xa_context.c

@@ -37,7 +37,11 @@
 XA_EXPORT void
 xa_context_flush(struct xa_context *ctx)
 {
-	ctx->pipe->flush(ctx->pipe, &ctx->last_fence, 0);
+    if (ctx->last_fence) {
+        struct pipe_screen *screen = ctx->xa->screen;
+        screen->fence_reference(screen, &ctx->last_fence, NULL);
+    }
+    ctx->pipe->flush(ctx->pipe, &ctx->last_fence, 0);
 }
 
 XA_EXPORT struct xa_context *

src/gallium/state_trackers/xa/xa_tracker.c

@@ -461,7 +461,7 @@ xa_surface_redefine(struct xa_surface *srf,
 			xa_min(save_height, template->height0), &src_box);
 	pipe->resource_copy_region(pipe, texture,
 				   0, 0, 0, 0, srf->tex, 0, &src_box);
-	pipe->flush(pipe, &xa->default_ctx->last_fence, 0);
+	xa_context_flush(xa->default_ctx);
     }
 
     pipe_resource_reference(&srf->tex, texture);

src/gallium/state_trackers/xa/xa_yuv.c

@@ -154,7 +154,7 @@ xa_yuv_planar_blit(struct xa_context *r,
 	box++;
     }
 
-    r->pipe->flush(r->pipe, &r->last_fence, 0);
+    xa_context_flush(r);
 
     xa_ctx_sampler_views_destroy(r);
     xa_ctx_srf_destroy(r);