NVDEC implementation using FFmpeg (#443)

* Initial nvdec implementation using FFmpeg

* Fix swapped channels on the video decoder and the G8R8 texture format

* Fix texture samplers not being set properly (regression)

* Rebased

* Remove unused code introduced on the rebase

* Add support for RGBA8 output format on the video image composer

* Correct spacing

* Some fixes for rebase and other tweaks

* Allow size mismatch on frame copy

* Get rid of GetHostAddress calls on VDec

Ryujinx.Graphics/Graphics3d/Texture/ISwizzle.cs

@@ -0,0 +1,7 @@
+namespace Ryujinx.Graphics.Texture
+{
+    interface ISwizzle
+    {
+        int GetSwizzleOffset(int X, int Y);
+    }
+}