panfrost: Pin an architecture for blending

Need to pick something but it's all the same, even on Valhall.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11785>

src/panfrost/lib/pan_blend.c

@@ -32,6 +32,11 @@
 #include "compiler/nir/nir_conversion_builder.h"
 #include "compiler/nir/nir_lower_blend.h"
 
+/* Blending is shared across all supported Malis with only minor differences,
+ * so pin a particular version */
+#define ARCH 7
+#include <midgard_pack.h>
+
 /* Fixed function blending */
 
 static bool