Fix RV64 badaddr value on instruction faults with large addresses

We were relying on ALU passthrough for this, but failed to override the
ALU dw argument, so bits above 31 could be discarded.

rocket/src/main/scala/rocket.scala

@@ -322,6 +322,7 @@ class Rocket(implicit p: Parameters) extends CoreModule()(p) {
     ex_ctrl.csr := id_csr
     when (id_xcpt) { // pass PC down ALU writeback pipeline for badaddr
       ex_ctrl.alu_fn := ALU.FN_ADD
+      ex_ctrl.alu_dw := DW_XPR
       ex_ctrl.sel_alu1 := A1_PC
       ex_ctrl.sel_alu2 := A2_ZERO
       when (!bpu.io.xcpt_if && !ibuf.io.inst(0).bits.pf0 && ibuf.io.inst(0).bits.pf1) { // PC+2