ioport: pci: Move port allocations to PCI devices

The dynamic ioport allocation with IOPORT_EMPTY is currently only used
by PCI devices. Other devices use fixed ports for which they request
registration to the ioport API.

PCI ports need to be in the PCI IO space and there is no reason ioport
API should know a PCI port is being allocated and needs to be placed in
PCI IO space. This currently just happens to be the case.

Move the responsability of dynamic allocation of ioports from the ioport
API to PCI.

In the future, if other types of devices also need dynamic ioport
allocation, they'll have to figure out the range of ports they are
allowed to use.

Signed-off-by: Julien Thierry <julien.thierry@arm.com>
[Renamed functions for clarity]
Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>