pc-bios/s390-ccw: Remove panics from Netboot IPL path

Remove panic-on-error from Netboot specific functions so that error recovery
may be possible in the future.

Functions that would previously panic now provide a return code.

Signed-off-by: Jared Rossi <jrossi@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20241020012953.1380075-12-jrossi@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
4 files changed