Add 'tensor' bit to commit_if and writeback_if

For use in the asynchronous tensor instruction.  When 1'b1, sets/unsets
the inuse_tensor status bit in the scoreboard to signal
kickoff/completion of the asynchronous tensor op.

hw/rtl/interfaces/VX_writeback_if.sv

@@ -22,6 +22,7 @@ interface VX_writeback_if import VX_gpu_pkg::*; ();
         logic [`XLEN-1:0]               PC;
         logic [`NR_BITS-1:0]            rd;
         logic [`NUM_THREADS-1:0][`XLEN-1:0] data;
+        logic                           tensor;
         logic                           sop;
         logic                           eop;
     } data_t;