Exchange libav with ffmpeg submodule.

.gitmodules

@@ -7,9 +7,6 @@
 [submodule "third_party/binutils-ppc-cygwin"]
 	path = third_party/binutils-ppc-cygwin
 	url = https://github.com/benvanik/binutils-ppc-cygwin.git
-[submodule "third_party/libav"]
-	path = third_party/libav
-	url = https://github.com/xenia-project/libav.git
 [submodule "third_party/spirv-tools"]
 	path = third_party/spirv-tools
 	url = https://github.com/xenia-project/SPIRV-Tools.git
@@ -76,3 +73,6 @@
 [submodule "third_party/xxhash"]
 	path = third_party/xxhash
 	url = https://github.com/Cyan4973/xxHash.git
+[submodule "third_party/FFmpeg"]
+	path = third_party/FFmpeg
+	url = https://github.com/xenia-project/FFmpeg.git

premake5.lua

@@ -230,10 +230,10 @@ solution("xenia")
   include("third_party/discord-rpc.lua")
   include("third_party/cxxopts.lua")
   include("third_party/cpptoml.lua")
+  include("third_party/FFmpeg/premake5.lua")
   include("third_party/fmt.lua")
   include("third_party/glslang-spirv.lua")
   include("third_party/imgui.lua")
-  include("third_party/libav.lua")
   include("third_party/mspack.lua")
   include("third_party/snappy.lua")
   include("third_party/spirv-tools.lua")

third_party/libav.lua

@@ -1,3 +0,0 @@
-group("third_party")
-  include("libav/libavcodec/premake5.lua")
-  include("libav/libavutil/premake5.lua")