memory: Add RasterizerMarkRegionCached code and cleanup.

src/core/memory.h

@@ -254,6 +254,11 @@ enum class FlushMode {
     FlushAndInvalidate,
 };
 
+/**
+ * Mark each page touching the region as cached.
+ */
+void RasterizerMarkRegionCached(VAddr start, u64 size, bool cached);
+
 /**
  * Flushes and invalidates any externally cached rasterizer resources touching the given virtual
  * address region.