The FpRegister size was miswritten as kSimd128Size like x64, while it
should be kDoubleSize on mips.

Change-Id: Iac4c5687e398a87ec0508fb99042a487c41ddf8c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2110891
Auto-Submit: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66804}