ctrl: Update formal to fix on new yosys

This was failing on newer versions of yosys.  The assert is
not true when we are testing the control unit alone as any
input can come in, we update to only check this for CPU level tests.

Also we remove the spr_access_valid assert which is just checking the
properties of an assign.

Author: stffrdhrn

rtl/verilog/mor1kx_ctrl_cappuccino.v

@@ -1624,14 +1624,11 @@ endgenerate
       if (f_past_valid && !$past(rst) && $rose(ctrl_bubble_o))
          assert ($past(execute_bubble_i));
 
+`ifndef CTRL
    //SPR shouldn't give more than one acknowledgement
    always @*
       assert ($onehot0(spr_access_ack));
-
-   //SPR acknowledgement makes spr access valid
-   always @*
-      if ($onehot(spr_access_ack))
-         assert (spr_access_valid);
+`endif
 
    //Insn mfspr should always read from spr and
    //insn mtspr should always write to spr.