[S390] IRQs too early enabled.

setup_lowcore() calls ctl_set_bit() which returns withs interrupts
enabled. The setup arch code is not supposed to enable interrupts that
early. Therefore use the __ctl_set_bit() variant.
This fixes the not working lock dependency validator on non 64 bit
systems.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>