pc-bios: s390x: Move panic() into header and add infinite loop

panic() was defined for the ccw and net bios, i.e. twice, so it's
cleaner to rather put it into the header.

Also let's add an infinite loop into the assembly of disabled_wait() so
the caller doesn't need to take care of it.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20200624075226.92728-9-frankja@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>