broadcom/compiler: track pending ldtmu count with each TMU lookup

And use this information when scheduling QPU to avoid merging
a new TMU request into a previous ldtmu instruction when doing
so may cause TMU output fifo overflow due to a stalling ldtmu.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22044>

src/broadcom/compiler/v3d_compiler.h

@@ -173,6 +173,11 @@ struct qinst {
         /* If this is a a TLB Z write */
         bool is_tlb_z_write;
 
+        /* If this is a retiring TMU instruction (the last in a lookup sequence),
+         * how many ldtmu instructions are required to read the results.
+         */
+        uint32_t ldtmu_count;
+
         /* Position of this instruction in the program. Filled in during
          * register allocation.
          */