Only use persistent buffers to flush on NVIDIA and Windows+AMD (#2489)

It seems like this method of flushing data is much slower on Mesa drivers, and slightly slower on Intel Windows. Have not tested Intel Mesa, but I'm assuming it is the same as AMD.

This also adds vendor detection for AMD on Unix, which counted as "Unknown" before.

Ryujinx.Graphics.OpenGL/PersistentBuffers.cs

@@ -63,15 +63,8 @@ namespace Ryujinx.Graphics.OpenGL
             GL.DeleteSync(sync);
         }
 
-        public byte[] GetTextureData(TextureView view)
+        public byte[] GetTextureData(TextureView view, int size)
         {
-            int size = 0;
-
-            for (int level = 0; level < view.Info.Levels; level++)
-            {
-                size += view.Info.GetMipSize(level);
-            }
-
             EnsureBuffer(size);
 
             GL.BindBuffer(BufferTarget.PixelPackBuffer, _copyBufferHandle);