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/ChSubmissionMode.cs

@@ -0,0 +1,13 @@
+namespace Ryujinx.Graphics
+{
+    enum ChSubmissionMode
+    {
+        SetClass        = 0,
+        Incrementing    = 1,
+        NonIncrementing = 2,
+        Mask            = 3,
+        Immediate       = 4,
+        Restart         = 5,
+        Gather          = 6
+    }
+}