GPU: Implemented register 0x22A.

This is the equivalent of the "first" parameter in glDrawArrays, it tells the GPU the vertex index at which to start rendering.

Register 0x22A doesn't affect indexed rendering.

src/video_core/pica.h

@@ -757,7 +757,12 @@ struct Regs {
     // Number of vertices to render
     u32 num_vertices;
 
-    INSERT_PADDING_WORDS(0x5);
+    INSERT_PADDING_WORDS(0x1);
+
+    // The index of the first vertex to render
+    u32 vertex_offset;
+
+    INSERT_PADDING_WORDS(0x3);
 
     // These two trigger rendering of triangles
     u32 trigger_draw;