PCI: Add pci_remap_iospace() to map bus I/O resources

Add pci_remap_iospace() to map bus I/O resources into the CPU virtual
address space.  Architectures with special needs may provide their own
version, but most should be able to use this one.

This function is useful for PCI host bridge drivers that need to map the
PCI I/O resources into virtual memory space.

[bhelgaas: phys_addr description, drop temporary "err" variable]
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
CC: Arnd Bergmann <arnd@arndb.de>