maxwell_3d: Add a struct for RenderTargetConfig.

src/video_core/engines/maxwell_3d.h

@@ -321,19 +321,7 @@ public:
             INSERT_PADDING_WORDS(1);
         };
 
-        union {
+        struct RenderTargetConfig {
-            struct {
-                INSERT_PADDING_WORDS(0x45);
-
-                struct {
-                    INSERT_PADDING_WORDS(1);
-                    u32 data;
-                    u32 entry;
-                } macros;
-
-                INSERT_PADDING_WORDS(0x1B8);
-
-                struct {
             u32 address_high;
             u32 address_low;
             u32 width;
@@ -349,7 +337,21 @@ public:
                 return static_cast<GPUVAddr>((static_cast<GPUVAddr>(address_high) << 32) |
                                              address_low);
             }
-                } rt[NumRenderTargets];
+        };
+
+        union {
+            struct {
+                INSERT_PADDING_WORDS(0x45);
+
+                struct {
+                    INSERT_PADDING_WORDS(1);
+                    u32 data;
+                    u32 entry;
+                } macros;
+
+                INSERT_PADDING_WORDS(0x1B8);
+
+                RenderTargetConfig rt[NumRenderTargets];
 
                 struct {
                     f32 scale_x;