s390/topology: get rid of core mask array

Use a single long value instead of a single element array to represent
the core mask. The array is a leftover from 32/31 bit code so we were
able to use bitops helper functions.

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