This reverts commit 9caf26b9.

Reason for revert: Needed to be changed to kNumCallerSavedDoubles

Original change's description:
> S390: fix byte count when pushing/popping doubles
>
> `NumRegs` runs a `population count` and must be used with
> a `RegList` and not with a regular integer value.
>
> kCallerSavedDoubles is a regular integer and should be used as is.
>
> Change-Id: Id9535134ad4ea02bebed9b506012084d93acc2c2
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2965159
> Reviewed-by: Junliang Yan <junyan@redhat.com>
> Commit-Queue: Milad Fa <mfarazma@redhat.com>
> Cr-Commit-Position: refs/heads/master@{#75213}

Change-Id: Ifae6ee99b698f5a1f68a7c42cda1743fd1cbf0d7
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2969623
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/master@{#75223}