arm,kern: Use GuestABI to call printk from the kernel.

arm,kern: Use GuestABI to call printk from the kernel.

Change-Id: I07b0f1c01f5ec8d6761903fa4aa15b9e8ae35069
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/24113
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>