x86: dtb: Add support for PCI devices backed by dtb nodes

x86_of_pci_init() does two things:

- it provides a generic irq enable and disable function. enable queries
  the device tree for the interrupt information, calls ->xlate on the
  irq host and updates the pci->irq information for the device.

- it walks through PCI bus(es) in the device tree and adds its children
  (device) nodes to appropriate pci_dev nodes in kernel. So the dtb
  node information is available at probe time of the PCI device.

Adding a PCI bus based on the information in the device tree is
currently not supported. Right now direct access via ioports is used.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Dirk Brandewie <dirk.brandewie@gmail.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Cc: sodaville@linutronix.de
Cc: devicetree-discuss@lists.ozlabs.org
LKML-Reference: <1298405266-1624-8-git-send-email-bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>