pan/bi: Model writemasks correctly

We don't handle partial write masks in the backend yet, so for now we
can't pretend we do, else we'll have RA bugs. Fixes

dEQP-GLES2.functional.fragment_ops.blend.rgb_func_alpha_func.src.constant_color_dst_alpha

Fixes: b2c6cf2b6db1 ("pan/bi: Eliminate writemasks in the IR")
Cc: 20.3 <mesa-stable>
Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reported-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Tested-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7527>
(cherry picked from commit 7737ca75391d5ea930390037178a277d309a83af)
diff --git a/.pick_status.json b/.pick_status.json
index 815ce44..95aa3b4 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -1480,7 +1480,7 @@
         "description": "pan/bi: Model writemasks correctly",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "master_sha": null,
         "because_sha": "b2c6cf2b6db11eb2293f59b42dfeb3d7481477b0"
     },