s390/cio: use kmem_cache for extended measurement block allocation

Extended measurement blocks need to be 64 byte aligned. To achieve that
128 bytes for each measurement block are allocated and an align callback
returns a 64 byte aligned address inside this area.

Replace this code with kmem_cache allocations.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>