hvc_iucv: allocate memory buffers for IUCV in zone DMA

hvc_iucv: allocate memory buffers for IUCV in zone DMA

commit 91a970d9889c7d6f451ee91ed361d0f0119d3778 upstream.

The device driver must allocate memory for IUCV buffers with GFP_DMA,
because IUCV cannot address memory above 2GB (31bit addresses only).

Because the IUCV ignores the higher bits of the address, sending and
receiving IUCV data with this driver might cause memory corruptions.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: maximilian attems <max@stro.at>