libavcodec/qsvenc: Let runtime to set default parameter.

Unset qsv_h264 and qsv_hevc's default settings. Let runtime to decide
these parameters, so that it can choose the best parameter and ffmpeg-qsv
can keep up with runtime's update.

Signed-off-by: Wenbin Chen <wenbin.chen@intel.com>

libavcodec/qsvenc_h264.c

@@ -176,9 +176,8 @@ static const AVClass class = {
 static const FFCodecDefault qsv_enc_defaults[] = {
     { "b",         "1M"    },
     { "refs",      "0"     },
-    // same as the x264 default
-    { "g",         "250"   },
-    { "bf",        "3"     },
+    { "g",         "-1"    },
+    { "bf",        "-1"    },
     { "qmin",      "-1"    },
     { "qmax",      "-1"    },
     { "trellis",   "-1"    },

libavcodec/qsvenc_hevc.c

@@ -289,8 +289,7 @@ static const AVClass class = {
 static const FFCodecDefault qsv_enc_defaults[] = {
     { "b",         "1M"    },
     { "refs",      "0"     },
-    // same as the x264 default
-    { "g",         "248"   },
+    { "g",         "-1"    },
     { "bf",        "-1"    },
     { "qmin",      "-1"    },
     { "qmax",      "-1"    },