ARM/PCI: Move align_resource function pointer to pci_host_bridge structure

Commit b3a72384

 ("ARM/PCI: Replace pci_sys_data->align_resource with
global function pointer") introduced an ARM-specific align_resource()
function pointer.  This is not portable to other arches and doesn't work
for platforms with two different PCIe host bridge controllers.

Move the function pointer to the pci_host_bridge structure so each host
bridge driver can specify its own align_resource() function.

Signed-off-by: Gabriele Paoloni <gabriele.paoloni@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>