For tail calls, we already set the flag kCallTail on CallBufferFlags,
the bool is_tail_cal always matches the flag (and there is only one call
site (L3037).

Drive-by clean up to get SaveFPRegsMode once, this is used when we need
to save and restore caller-saved registers.

Change-Id: Id175922c4cb5162d38b5ab61b84e151aaf2083e8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2945536Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75056}