pan/bi: Add slot to bi_instr

For better handling of message-passing instructions.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16804>

src/panfrost/bifrost/compiler.h

@@ -390,6 +390,9 @@ typedef struct {
         /* Flow control associated with a Valhall instruction */
         uint8_t flow;
 
+        /* Slot associated with a message-passing instruction */
+        uint8_t slot;
+
         /* Can we spill the value written here? Used to prevent
          * useless double fills */
         bool no_spill;