arch: Switch SyscallDescABI in for SyscallDesc.

arch: Switch SyscallDescABI in for SyscallDesc.

This lets system calls accept arguments by putting them in their
signatures.

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

Change-Id: Ieb32b8b5592d894e493466717613ff16e2a03768
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23191
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>