s390/pci: resize iomap

s390/pci: resize iomap

BugLink: http://bugs.launchpad.net/bugs/1558624
On s390 we need to maintain a mapping between iomem addresses
and arch specific function identifiers. Currently the mapping
table is created as such that we could span the whole iomem
address space. Since we can only map each bar space from each
possible function we have an upper bound for the number of
mapping entries.

This reduces the size of the iomap from 256K to less than 4K
(using the defconfig).

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
(cherry picked from commit c506fff3d3a8a632e8eb2270680548ec415f0357)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>