pc-bios/s390-ccw: Use the libc from SLOF and remove sclp prints

pc-bios/s390-ccw: Use the libc from SLOF and remove sclp prints

We are already using the libc from SLOF for the s390-netboot.img, and
this libc implementation is way more complete and accurate than the
simple implementation that we currently use for the s390-ccw.img binary.
Since we are now always assuming that the SLOF submodule is available
when building the s390-ccw bios (see commit bf6903f6944f), we can drop
the simple implementation and use the SLOF libc for the s390-ccw.img
binary, too.

Additionally replace sclp_print calls with puts/printf now that it is
available.

Co-authored by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Jared Rossi <jrossi@linux.ibm.com>
Message-ID: <20241020012953.1380075-3-jrossi@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>