target: arm: ignore invalid aarch64 msr/mrs instructions

Author: zhuowei

target/arm/translate-a64.c

@@ -1577,7 +1577,8 @@ static void handle_sys(DisasContext *s, uint32_t insn, bool isread,
         qemu_log_mask(LOG_UNIMP, "%s access to unsupported AArch64 "
                       "system register op0:%d op1:%d crn:%d crm:%d op2:%d\n",
                       isread ? "read" : "write", op0, op1, crn, crm, op2);
-        unallocated_encoding(s);
+        // zhuowei: just ignore
+        // unallocated_encoding(s);
         return;
     }