pc-bios/s390-ccw: Enable failed IPL to return after error

pc-bios/s390-ccw: Enable failed IPL to return after error

Remove panic-on-error from IPL functions such that a return code is propagated
back to the main IPL calling function (rather than terminating immediately),
which facilitates possible error recovery in the future.

A select few panics remain, which indicate fatal non-devices errors that must
result in termination.

Signed-off-by: Jared Rossi <jrossi@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20241020012953.1380075-13-jrossi@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>