PCI: Add PCI_BUS_NUM() and PCI_DEVID() interfaces

PCI defines PCI_DEVFN(), PCI_SLOT(), and PCI_FUNC() interfaces; however,
it doesn't have interfaces to return PCI bus and PCI device id. Drivers
(AMD IOMMU, and AER) implement module specific definitions for PCI_BUS()
and AMD_IOMMU driver also has a module specific interface to calculate PCI
device id from bus number and devfn.

Add PCI_BUS_NUM and PCI_DEVID interfaces to return PCI bus number and PCI
device id respectively to avoid the need for duplicate definitions in other
modules. AER driver code and AMD IOMMU driver define PCI_BUS. AMD IOMMU
driver defines an interface to calculate device id from bus number, and
devfn pair.

PCI_DEVFN(), PCI_SLOT(), and PCI_FUNC() interfaces are exported to
user-space via uapi/linux/pci.h. However, in the interest to keep the new
interfaces as kernel only and not export them to user-space unnecessarily,
added them to linux/pci.h instead.

Signed-off-by: Shuah Khan <shuah.khan@hp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Joerg Roedel <joro@8bytes.org>