s390/airq: use DMA memory for summary indicators

Protected virtualization guests have to use shared pages for airq
notifier bit vectors and summary bytes or bits, thus these need to be
allocated as DMA coherent memory.  Commit b50623e5 ("s390/airq: use
DMA memory for adapter interrupts")  took care of the notifier bit
vectors, but omitted to take care of the summary bytes/bits.

In practice this omission is not a big deal, because the summary ain't
necessarily allocated here, but can be supplied by the driver. Currently
all the I/O we have for SE guests is virtio-ccw, and  virtio-ccw uses a
self-allocated array of summary indicators.

Let us cover all our bases nevertheless!

Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>