[Enhancement] Offload transformer after switch to transformer-2 (#3224)

Signed-off-by: Chendi Xue <chendi.xue@intel.com>
Co-authored-by: Canlin Guo <canlinguosdu@gmail.com>

docs/user_guide/diffusion/cpu_offload_diffusion.md

@@ -17,7 +17,7 @@ Both strategies use pinned memory for faster CPU-GPU transfers. The strategies a
 Model-level offloading implements mutual exclusion between DiT transformer and encoder modules using pre forward hooks:
 
 - **When encoders run**: DiT transformer is offloaded to CPU
-- **When DiT runs**: Encoders are offloaded to CPU
+- **When DiT runs**: Encoders are offloaded to CPU, if more than one dit models, only one loaded on GPU, others get offloaded to CPU.
 - **VAE**: Stays resident on GPU
 
 Before each module's forward pass, the hook automatically moves it to GPU while offloading the other module group to CPU. Transfers use pinned memory for speed.