Allows atomic loading of an unsigned 32bit value from 64bit widths.

Bug: v8:12093
Change-Id: Ib6ca2f3f44d4e82e5e41bf1ca0494e48ca90a21a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3096888Reviewed-by: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Auto-Submit: Liu yu <liuyu@loongson.cn>
Cr-Commit-Position: refs/heads/master@{#76307}