s390/qdio: add helpers to manage qdio buffers

Users of qdio buffers employ different strategies to manage these
buffers. The qeth driver uses huge contiguous buffers which leads
to high order allocations with all their downsides.

This patch provides helpers to allocate, free, and reset arrays of
qdio buffers using non contiguous pages.

Reviewed-by: Martin Peschke <mpeschke@linux.vnet.ibm.com>
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>