microblaze: Trap if QEMU finds an unknown insns.

If PVR settings enable illegal insn trap, trap when QEMU finds an
insn it knows nothing about.
Signed-off-by: NEdgar E. Iglesias <edgar.iglesias@gmail.com>

target-microblaze/translate.c

@@ -1144,6 +1144,12 @@ static void dec_fpu(DisasContext *dc)
 
 static void dec_null(DisasContext *dc)
 {
+    if ((dc->tb_flags & MSR_EE_FLAG)
+          && (dc->env->pvr.regs[2] & PVR2_ILL_OPCODE_EXC_MASK)) {
+        tcg_gen_movi_tl(cpu_SR[SR_ESR], ESR_EC_ILLEGAL_OP);
+        t_gen_raise_exception(dc, EXCP_HW_EXCP);
+        return;
+    }
     qemu_log ("unknown insn pc=%x opc=%x\n", dc->pc, dc->opcode);
     dc->abort_at_next_insn = 1;
 }