[3PP] Switch FFmpeg to latest release with port of xmaframes codec

And pull out all the xenia specific build junk into
third_party/ffmpeg-xenia rather than keeping it checked in the
submodule

third_party/ffmpeg-xenia/libavformat/premake5.lua

@@ -0,0 +1,61 @@
+project("libavformat")
+  uuid("CEF2E128-AA08-4A36-8045-0AA68A556364")
+  kind("StaticLib")
+  language("C")
+  ffmpeg_common()
+
+  filter("files:not wmaprodec.c")
+    warnings "Off"
+  filter({})
+
+  links({
+    "libavutil",
+    "libavcodec",
+  })
+
+  -- libavformat/Makefile:
+  --   HEADERS:
+  files({
+    "../../FFmpeg/libavformat/avformat.h",
+    "../../FFmpeg/libavformat/avio.h",
+    "../../FFmpeg/libavformat/version.h",
+  })
+  --   OBJS:
+  files({
+    "../../FFmpeg/libavformat/allformats.c",
+    "../../FFmpeg/libavformat/avio.c",
+    "../../FFmpeg/libavformat/aviobuf.c",
+    "../../FFmpeg/libavformat/dump.c",
+    "../../FFmpeg/libavformat/format.c",
+    "../../FFmpeg/libavformat/id3v1.c",
+    "../../FFmpeg/libavformat/id3v2.c",
+    "../../FFmpeg/libavformat/metadata.c",
+    "../../FFmpeg/libavformat/mux.c",
+    "../../FFmpeg/libavformat/options.c",
+    "../../FFmpeg/libavformat/os_support.c",
+    "../../FFmpeg/libavformat/protocols.c",
+    "../../FFmpeg/libavformat/riff.c",
+    "../../FFmpeg/libavformat/sdp.c",
+    "../../FFmpeg/libavformat/url.c",
+    "../../FFmpeg/libavformat/utils.c",
+    "../../FFmpeg/libavformat/riffdec.c",
+    "../../FFmpeg/libavformat/asfdec_f.c",
+    "../../FFmpeg/libavformat/asf.c",
+    "../../FFmpeg/libavformat/asfcrypt.c",
+    "../../FFmpeg/libavformat/avlanguage.c",
+    "../../FFmpeg/libavformat/mp3dec.c",
+    "../../FFmpeg/libavformat/replaygain.c",
+    "../../FFmpeg/libavformat/file.c",
+    "../../FFmpeg/libavformat/demux.c",
+    "../../FFmpeg/libavformat/avformat.c",
+    "../../FFmpeg/libavformat/seek.c",
+    "../../FFmpeg/libavformat/demux_utils.c",
+    "../../FFmpeg/libavformat/urldecode.c",
+    "../../FFmpeg/libavformat/asf_tags.c",
+    "../../FFmpeg/libavformat/to_upper4.c",
+  })
+  filter({"platforms:Windows"})
+  files({
+    "../../FFmpeg/libavformat/file_open.c",
+  })
+  filter({})