[S390] appldata/extmem/kvm: add missing GFP_KERNEL flag

Add missing GFP flag to memory allocations. The part in cio only
changes a comment.

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