qsv: Make the hevc idr_interval consistent with the h264 one

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.

libavcodec/qsvenc_hevc.c

@@ -181,6 +181,9 @@ static av_cold int qsv_enc_init(AVCodecContext *avctx)
         }
     }
 
+    // HEVC and H264 meaning of the value is shifted by 1, make it consistent
+    q->qsv.idr_interval++;
+
     ret = ff_qsv_enc_init(avctx, &q->qsv);
     if (ret < 0)
         return ret;
@@ -220,7 +223,8 @@ static av_cold int qsv_enc_close(AVCodecContext *avctx)
 static const AVOption options[] = {
     QSV_COMMON_OPTS
 
-    { "idr_interval", "Distance (in I-frames) between IDR frames", OFFSET(qsv.idr_interval), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, VE },
+    { "idr_interval", "Distance (in I-frames) between IDR frames", OFFSET(qsv.idr_interval), AV_OPT_TYPE_INT, { .i64 = 0 }, -1, INT_MAX, VE, "idr_interval" },
+    { "begin_only", "Output an IDR-frame only at the beginning of the stream", 0, AV_OPT_TYPE_CONST, { .i64 = -1 }, 0, 0, VE, "idr_interval" },
     { "load_plugin", "A user plugin to load in an internal session", OFFSET(load_plugin), AV_OPT_TYPE_INT, { .i64 = LOAD_PLUGIN_DEFAULT }, LOAD_PLUGIN_NONE, LOAD_PLUGIN_HEVC_HW, VE, "load_plugin" },
     { "none",     NULL, 0, AV_OPT_TYPE_CONST, { .i64 = LOAD_PLUGIN_NONE },    0, 0, VE, "load_plugin" },
     { "hevc_sw",  NULL, 0, AV_OPT_TYPE_CONST, { .i64 = LOAD_PLUGIN_HEVC_SW }, 0, 0, VE, "load_plugin" },