Drive-by edit to use ASM_CODE_COMMENT for better code comments for
all the more complicated macro-assembler functions.

Also undef macros (AVX_OP et al) since they are not longer used outside
of shared-macro-assembler.

Bug: v8:11589
Change-Id: I424f27b5b742a8efb26ccef87dbffb01eae60335
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3173892Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76973}