PCI: generic: Convert to DT resource parsing API

In order to consolidate DT configuration for PCI host controllers in the
kernel, a new API, of_pci_get_host_bridge_resources(), was developed to
allow parsing and assigning IO/BUS/MEM resources from DT, removing
duplicated code present in the majority of PCI host driver implementations.

Convert the existing PCI generic host controller driver to the new API.
Most of the code parsing ranges and creating resources is now delegated to
the of_pci_get_host_bridge_resources() API.

The PCI host controller code filters the resulting resource list and maps
IO space by using the newly introduced pci_ioremap_iospace() API.

New code supports only one IO resource per generic host controller, which
should cater for all existing host controller configurations.

[bhelgaas: changelog]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Will Deacon <will.deacon@arm.com>