[rtl] RVFI changes and extensions for co-simulation

This adds some new `rvfi_ext` signals that are needed by the
co-simulation environment.

It also fixes/alters `rvfi_trap`. Previously it wouldn't work correctly
in various cases. Now it is fully functional, though it's meaning
includes more trap cases than the RVFI spec strictly includes. It is now
set for any instruction that produces a synchronous trap (everything bar
interrupts).

Author: GregAC

rtl/ibex_controller.sv

@@ -353,7 +353,7 @@ module ibex_controller #(
   always_comb begin : gen_mfip_id
     mfip_id = 4'd0;
 
-    for (int i = 14;i >= 0; i--) begin
+    for (int i = 14; i >= 0; i--) begin
       if (irqs_i.irq_fast[i]) begin
         mfip_id = i[3:0];
       end
@@ -936,4 +936,12 @@ module ibex_controller #(
     `ASSERT(IbexNoPCSetOnSpecialReqIfNotExpected,
       exception_req_pending && !expect_exception_pc_set |-> ~pc_set_o)
   `endif
+
+  `ifdef RVFI
+    // Workaround for internal verilator error when using hierarchical refers to calcuate this
+    // directly in ibex_core
+    logic rvfi_flush_next;
+
+    assign rvfi_flush_next = ctrl_fsm_ns == FLUSH;
+  `endif
 endmodule