Changes device of given mxnet arguments
    :param arg_params: arguments
    :param aux_params: auxiliary parameters
    :param ctx: new device context
    :return: arguments and auxiliary parameters on new device

def _ch_dev(arg_params, aux_params, ctx):
    """
    Changes device of given mxnet arguments
    :param arg_params: arguments
    :param aux_params: auxiliary parameters
    :param ctx: new device context
    :return: arguments and auxiliary parameters on new device
    """
    new_args = dict()
    new_auxs = dict()
    for k, v in arg_params.items():
        new_args[k] = v.as_in_context(ctx)
    for k, v in aux_params.items():
        new_auxs[k] = v.as_in_context(ctx)
    return new_args, new_auxs