s390/numa: allocate memory with correct alignment

Allocating memory with a requested minimum alignment of 1 is wrong
since pg_data_t contains a spinlock which requires an alignment of 4
bytes.

Therefore fix this and ask for an alignment of 8 bytes like it is
guarenteed for all kmalloc requests.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>