Given two registers that are both not gp_pair, one could be an fp_pair,
and the other not, and we will incorrect call == on them. The current
check needs to be expanded to check that both registers are fp_pair.

Bug: chromium:1054466
Change-Id: Ib986c002a8a5cadb9668458597a797cecfd971b1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2070006
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66402}