CNS3xxx: Remove artificial dependency on pci_sys_data domain.

On cns3xxx platforms the PCI controller probing code relies on an
artificial dependency on the domain number to look-up the internal data
structures.

This patch reworks the host controller control data structure and adds a
domain equivalent field named port in it so that the dependency on
pci_sys_data domain field can be eventually removed.

Acked-by: Krzysztof Hałasa <khalasa@piap.pl>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[lp: added commit log, removed pci_sys_data domain references]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>