ggml: Add POOL2D OP for GPU acceleration to the Vulkan backend in the MobileVLM model...

ggml: Add POOL2D OP for GPU acceleration to the Vulkan backend in the MobileVLM model. (llama/9763)

* ggml: Add POOL2D OP for GPU ACC to the Vulkan.

- The MobileVLM model now supports inference acceleration through GPU by utilizing the Vulkan backend.
- A GGML_OP_POOL_2D shader has been added. (Pooling)
- The encoding performance of the CLIP model improved from 2.8s on the CPU to 0.7s on the GPU.

Signed-off-by: Changyeon Kim <redacted>
* [fix] Correct the incorrect order of the parameters.

fix casting to int.

Signed-off-by: Changyeon Kim <redacted>
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Signed-off-by: Changyeon Kim <redacted>