s390/head: initialize all new psws

Initialize all new psws with disabled wait psws, except for the restart new
psw. This way every unexpected exception, svc, machine check, or interrupt
is handled properly.

Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>