panfrost: Rename unknown2_8 to padding

It's zero everywhere.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3835>

src/panfrost/include/panfrost-job.h

@@ -614,8 +614,7 @@ struct mali_shader_meta {
                 } midgard2;
         };
 
-        /* zero on bifrost */
-        u32 unknown2_8;
+        u32 padding;
 
         /* Blending information for the older non-MRT Midgard HW. Check for
          * MALI_HAS_BLEND_SHADER to decide how to interpret.

src/panfrost/pandecode/decode.c

@@ -2270,8 +2270,10 @@ pandecode_vertex_tiler_postfix_pre(
                         pandecode_log("},\n");
                 }
 
-                if (s->unknown2_8)
-                        pandecode_prop("unknown2_8 = 0x%" PRIx32, s->unknown2_8);
+                if (s->padding) {
+                        pandecode_msg("XXX: shader padding tripped\n");
+                        pandecode_prop("padding = 0x%" PRIx32, s->padding);
+                }
 
                 if (!is_bifrost) {
                         /* TODO: Blend shaders routing/disasm */