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/VDec/H264BitStreamWriter.cs

@@ -0,0 +1,79 @@
+using System.IO;
+
+namespace Ryujinx.Graphics.VDec
+{
+    class H264BitStreamWriter : BitStreamWriter
+    {
+        public H264BitStreamWriter(Stream BaseStream) : base(BaseStream) { }
+
+        public void WriteU(int Value, int ValueSize)
+        {
+            WriteBits(Value, ValueSize);
+        }
+
+        public void WriteSe(int Value)
+        {
+            WriteExpGolombCodedInt(Value);
+        }
+
+        public void WriteUe(int Value)
+        {
+            WriteExpGolombCodedUInt((uint)Value);
+        }
+
+        public void End()
+        {
+            WriteBit(true);
+
+            Flush();
+        }
+
+        private void WriteExpGolombCodedInt(int Value)
+        {
+            int Sign = Value <= 0 ? 0 : 1;
+
+            if (Value < 0)
+            {
+                Value = -Value;
+            }
+
+            Value = (Value << 1) - Sign;
+
+            WriteExpGolombCodedUInt((uint)Value);
+        }
+
+        private void WriteExpGolombCodedUInt(uint Value)
+        {
+            int Size = 32 - CountLeadingZeros((int)Value + 1);
+
+            WriteBits(1, Size);
+
+            Value -= (1u << (Size - 1)) - 1;
+
+            WriteBits((int)Value, Size - 1);
+        }
+
+        private static readonly byte[] ClzNibbleTbl = { 4, 3, 2, 2, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0 };
+
+        private static int CountLeadingZeros(int Value)
+        {
+            if (Value == 0)
+            {
+                return 32;
+            }
+
+            int NibbleIdx = 32;
+            int PreCount, Count = 0;
+
+            do
+            {
+                NibbleIdx -= 4;
+                PreCount = ClzNibbleTbl[(Value >> NibbleIdx) & 0b1111];
+                Count += PreCount;
+            }
+            while (PreCount == 4);
+
+            return Count;
+        }
+    }
+}