Kernel/Graphics: Increase VirtIO GPU transfer buffer size to 4MiB

This is necessary to allow transferring frame buffers larger than
~500x500 pixels back to user space. Until the buffer management is
improved this allows us to at least test the existing game ports.

Kernel/Graphics/VirtIOGPU/GPU3DDevice.h

@@ -139,7 +139,7 @@ private:
     HashMap<OpenFileDescription*, LockRefPtr<PerContextState>> m_context_state_lookup;
     // Memory management for backing buffers
     NonnullOwnPtr<Memory::Region> m_transfer_buffer_region;
-    constexpr static size_t NUM_TRANSFER_REGION_PAGES = 256;
+    constexpr static size_t NUM_TRANSFER_REGION_PAGES = 1024;
 };
 
 }