fpu_wrap: Add missing default assignment for fpu_exception fields (#3292)

This PR proposes a fix for the issue #3256 by adding missing default assignments to the tval2, tinst, and gva fields of fpu_exception_o signal. These fields were left undriven, which led to X propagation during simulation.

---------

Co-authored-by: JeanRochCoulon <jean-roch.coulon@thalesgroup.com>

Author: IhsaneTahir

core/fpu_wrap.sv

@@ -562,6 +562,9 @@ module fpu_wrap
     assign fpu_exception_o.cause = {59'h0, fpu_status};
     assign fpu_exception_o.valid = 1'b0;
     assign fpu_exception_o.tval = '0;
+    assign fpu_exception_o.tval2 = '0;
+    assign fpu_exception_o.tinst = '0;
+    assign fpu_exception_o.gva = '0;
 
     // Downstream write port is dedicated to FPU and always ready
     assign fpu_out_ready = 1'b1;