llama: add LLAMA_API to deprecated llama_kv_self_seq_div (#14708)

Add LLAMA_API to fix the run-time error with llama-cpp-python in Windows env:
attributeError: function 'llama_kv_self_seq_div' not found.
Did you mean: 'llama_kv_self_seq_add'?

Although llama_kv_self_seq_div() has been marked deprecated but
it is necessary to export it to make llama-cpp-python happy.

Observed software version:
OS: windows
compiler: MSVC
llama-cpp-python: tag: v0.3.12-cu124
llama.cpp: tag: b5833

Signed-off-by: Min-Hua Chen <minhuadotchen@gmail.com>
Co-authored-by: Min-Hua Chen <minhua.chen@neuchips.ai>