[mips] Request to be an owner of MIPS files

I'm working for Loongson Technology, and I have contributed 120+
patches to maintain v8 on mips platform. I request to be an owner
of MIPS files, so that we can maintain mips ports more conveniently.

Change-Id: Ib01dadfb879fefe7c095398930573e8df0f7c8dd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2525542
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71332}

MIPS_OWNERS

 xwafish@gmail.com
+zhaojiazhong-hf@loongson.cn