PCI, of: Move PCI I/O space management to PCI core code

No functional changes in this patch.

PCI I/O space mapping code does not depend on OF; therefore it can be moved
to PCI core code.  This way we will be able to use it, e.g., in ACPI PCI
code.

Suggested-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Tomasz Nowicki <tn@semihalf.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Arnd Bergmann <arnd@arndb.de>
CC: Liviu Dudau <Liviu.Dudau@arm.com>