PCI: Fix bus resource assignment on 32 bits with 64b resources

The current pci_assign_unassigned_resources() code doesn't work properly
on 32 bits platforms with 64 bits resources. The main reason is the use
of unsigned long in various places instead of resource_size_t.

This is a pre-requisite for making powerpc use the generic code instead of
its own half-useful implementation.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>