Function div_ceil

dnn/src/common/utils.h:393–398

 */
template <typename int_t>
int_t div_ceil(int_t dividend, int_t divisor) {
    static_assert(std::is_integral<int_t>::value, "must be integers");
    megdnn_assert_internal(dividend >= 0);
    megdnn_assert_internal(divisor > 0);
    return (dividend + divisor - 1) / divisor;
}

/*!
 * \brief divide get result floored to int; both dividend and divisor shoud be