lavc/qsvenc: add support for external bitrate control for HEVC

Enables option for hevc_qsv encoder:
    -extbrc

Improvements in BD-Rate could be observed with extbrc on.

Signed-off-by: Linjie Fu <linjie.fu@intel.com>
Signed-off-by: Zhong Li <zhongli_dev@126.com>

libavcodec/qsvenc.c

@@ -687,11 +687,8 @@ FF_ENABLE_DEPRECATION_WARNINGS
 
         q->extparam_internal[q->nb_extparam_internal++] = (mfxExtBuffer *)&q->extco;
 
-        if (avctx->codec_id == AV_CODEC_ID_H264) {
 #if QSV_HAVE_CO2
-            q->extco2.Header.BufferId     = MFX_EXTBUFF_CODING_OPTION2;
+        if (avctx->codec_id == AV_CODEC_ID_H264) {
-            q->extco2.Header.BufferSz     = sizeof(q->extco2);
-
             if (q->int_ref_type >= 0)
                 q->extco2.IntRefType = q->int_ref_type;
             if (q->int_ref_cycle_size >= 0)
@@ -703,8 +700,6 @@ FF_ENABLE_DEPRECATION_WARNINGS
                 q->extco2.BitrateLimit = q->bitrate_limit ? MFX_CODINGOPTION_ON : MFX_CODINGOPTION_OFF;
             if (q->mbbrc >= 0)
                 q->extco2.MBBRC = q->mbbrc ? MFX_CODINGOPTION_ON : MFX_CODINGOPTION_OFF;
-            if (q->extbrc >= 0)
-                q->extco2.ExtBRC = q->extbrc ? MFX_CODINGOPTION_ON : MFX_CODINGOPTION_OFF;
 
             if (q->max_frame_size >= 0)
                 q->extco2.MaxFrameSize = q->max_frame_size;
@@ -752,9 +747,20 @@ FF_ENABLE_DEPRECATION_WARNINGS
                 q->extco2.MaxQPP = q->extco2.MaxQPB = q->extco2.MaxQPI;
             }
 #endif
+        }
+
+        if (avctx->codec_id == AV_CODEC_ID_H264 || avctx->codec_id == AV_CODEC_ID_HEVC) {
+            if (q->extbrc >= 0)
+                q->extco2.ExtBRC = q->extbrc ? MFX_CODINGOPTION_ON : MFX_CODINGOPTION_OFF;
+
+            q->extco2.Header.BufferId = MFX_EXTBUFF_CODING_OPTION2;
+            q->extco2.Header.BufferSz = sizeof(q->extco2);
+
             q->extparam_internal[q->nb_extparam_internal++] = (mfxExtBuffer *)&q->extco2;
+        }
 #endif
 
+        if (avctx->codec_id == AV_CODEC_ID_H264) {
 #if QSV_HAVE_MF
             if (QSV_RUNTIME_VERSION_ATLEAST(q->ver, 1, 25)) {
                 q->extmfp.Header.BufferId     = MFX_EXTBUFF_MULTI_FRAME_PARAM;