GPU: Discard data when getting texture before full clear (#5719)

* GPU: Discard data when getting texture before full clear

* Fix rules and order of clear checks

* Fix formatting

src/Ryujinx.Graphics.Gpu/Engine/Threed/RenderTargetUpdateFlags.cs

@@ -33,6 +33,11 @@ namespace Ryujinx.Graphics.Gpu.Engine.Threed
         /// </summary>
         UpdateDepthStencil = 1 << 3,
 
+        /// <summary>
+        /// Indicates that the data in the clip region can be discarded for the next use.
+        /// </summary>
+        DiscardClip = 1 << 4,
+
         /// <summary>
         /// Default update flags for draw.
         /// </summary>