8270832: Aarch64: Update algorithm annotations for MacroAssembler::fill_words

Co-authored-by: Wang Huang <whuang@openjdk.org>
Co-authored-by: Miu Zhuojun <mouzhuojun@huawei.com>
Co-authored-by: Wu Yan <wuyan@openjdk.org>
Reviewed-by: ngasson, aph