Restrictions in custom type name

It seems ‘x’ is wrong handled in custom datatype name. I came with custom name “complexfloat” and it is wrong split in python/tvm/_ffi/runtime_ctypes.py:123~125.

        arr = type_str.split("x")
        head = arr[0]
        self.lanes = int(arr[1]) if len(arr) > 1 else 1