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/NvGpuEngineP2mfReg.cs

@@ -1,17 +0,0 @@
-namespace Ryujinx.Graphics
-{
-    enum NvGpuEngineP2mfReg
-    {
-        LineLengthIn = 0x60,
-        LineCount    = 0x61,
-        DstAddress   = 0x62,
-        DstPitch     = 0x64,
-        DstBlockDim  = 0x65,
-        DstWidth     = 0x66,
-        DstHeight    = 0x67,
-        DstDepth     = 0x68,
-        DstZ         = 0x69,
-        DstX         = 0x6a,
-        DstY         = 0x6b
-    }
-}