s390/monwriter: do not use stack buffers for hardware data

With CONFIG_VMAP_STACK=y the stack is allocated from the vmalloc space.
Data structures passed to a hardware or a hypervisor interface that
requires V=R can not be allocated on the stack anymore.

Use kmalloc to get memory for the appldata_parameter_list and
appldata_product_id structures.

Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>