s390/smp,topology: add polarization member to pcpu struct

The cpu polarization member is the only per cpu state that is not part
of the pcpu structure. So add it there and have everything in one place.

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