s390/zcrypt: use kvmalloc instead of kmalloc for 256k alloc

Tests showed that it may happen that a 256k kmalloc may fail
due to a temporary shortage on 256k slab entries.

The find functions for cca and ep11 use a 256k array to fetch the
states of all possible crypto cards and their domains in one
piece. With the patch now kvmalloc is used to allocate this
temporary memory as there is no need to have this memory area
physical continuously.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>