According to the MediaSDK documentation the idr_interval value has
a different meaning depending on the codec:

    0 in H264 means make every I-frame IDR, in HEVC it means to have
    it only at the beginning.

    1 in H264 means every other I-frame is not-IDR, in HEVC it means
    that every I-frame is IDR.

Keep the behaviour consistent between the two encoders by increasing
by 1 internally the idr_interval value for HEVC.