s390/topology: remove offline CPUs from CPU topology masks

The CPU topology masks on s390 contain also bits of CPUs which
are offline. Currently this is already a problem, since common
code scheduler expects e.g. cpu_smt_mask() to reflect reality.

This update changes the described behaviour and s390 starts to
behave like all other architectures.

Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>