s390/qdio: avoid allocating the qdio_irq with GFP_DMA

The qdio_irq contains only two fields that are directly exposed to the
HW (ccw and qib). And only the ccw needs to reside in 31-bit memory. So
allocate it separately, and remove the GFP_DMA constraint from the
qdio_irq allocation.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>