Implement VMNMX shader instruction (#1032)

* Implement VMNMX shader instruction

* No need for the gap on the enum

* Fix typo

Ryujinx.Graphics.Shader/Decoders/VideoPostOp.cs

@@ -0,0 +1,14 @@
+namespace Ryujinx.Graphics.Shader.Decoders
+{
+    enum VideoPostOp
+    {
+        Mrg16h,
+        Mrg16l,
+        Mrg8b0,
+        Mrg8b2,
+        Acc,
+        Min,
+        Max,
+        Pass
+    }
+}