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/NvGpuEngine.cs

@@ -0,0 +1,11 @@
+namespace Ryujinx.Graphics.Graphics3d
+{
+    enum NvGpuEngine
+    {
+        _2d     = 0x902d,
+        _3d     = 0xb197,
+        Compute = 0xb1c0,
+        P2mf    = 0xa140,
+        M2mf    = 0xb0b5
+    }
+}