PCI: Add dummy pci_irqd_intx_xlate() for CONFIG_PCI=n build

Some hardware can operate in either "host" or "endpoint" mode, which means
there can be both a host bridge driver and an endpoint driver for the same
device.  Those drivers share a lot of code, so sometimes they live in the
same source file.

The host bridge driver requires CONFIG_PCI=y because it enumerates PCI
devices below the bridge using the PCI core.  The endpoint driver does not
require CONFIG_PCI=y because it runs in an embedded kernel on the other
side of the device, e.g., on an adapter card.

pci-dra7xx.c contains both host and endpoint drivers.  If we select only
the endpoint driver (CONFIG_PCI=n and CONFIG_PCI_DRA7XX_EP=y), the unneeded
host driver is still compiled.  It references pci_irqd_intx_xlate(), which
is not present when CONFIG_PCI=n, which causes this error:

  drivers/pci/dwc/pci-dra7xx.c:229:11: error: 'pci_irqd_intx_xlate' undeclared here (not in a function)

Add a dummy pci_irqd_intx_xlate() for the CONFIG_PCI=n case.

[bhelgaas: changelog]
Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>