PCI: fix pci_ioremap_bar() on s390

s390 doesn't have ioremap_*, so protect the definition of the new
pci_ioremap_bar function with CONFIG_HAS_IOMEM to avoid build breakage.

Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>