Jan 2 (Reuters) - Chinese internet search giant Baidu (BIDU) said on Friday its AI chip unit Kunlunxin has confidentially filed ​a listing application with the Hong Kong stock exchange on ‌January 1, paving the way for a spin-off and separate listing. Baidu's US shares rose 9% before the bell on Friday following the news. Reuters had earlier reported ‌that Kunlunxin was planning for a Hong Kong initial public offering after completing a fundraising that valued it at 21 billion yuan ($3 billion). China ...