Make "emit_s128_set_if_nan" take LiftoffRegisters rather than Registers.
The decoding of the FP register code is architecture dependent, and in
particular we expect an FP pair on arm.

R=clemensb@chromium.org

Bug: v8:11856
Change-Id: I44a364c3ef3a0c41000ea1f6cead4916ee04145d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3089165Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76246}