sim: Use variadic GuestABI arguments in a few additional syscalls.

Jira Issue: https://gem5.atlassian.net/browse/GEM5-187

Change-Id: Ib2f193e7409859469c853e11f121eba82b3c0ddc
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23196
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>