pan/bi: Add source/destination counts

In preparation for dynamic allocation, as needed for phi nodes and parallel
copies. For now, it just serves to simplify the semantics of splits and
collects.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16585>

src/panfrost/bifrost/compiler.h

@@ -379,6 +379,8 @@ typedef struct {
         struct list_head link;
 
         enum bi_opcode op;
+        uint8_t nr_srcs;
+        uint8_t nr_dests;
 
         /* Data flow */
         bi_index dest[BI_MAX_DESTS];