The devicetree binding documentation for the Xilinx NWL PCIe root port
bridge shows an example which uses an interrupt-map property to map PCI
INTx interrupts to hardware IRQ numbers 1-4. The driver creates an IRQ
domain with size 4, which therefore covers the hwirq range 0-3.

This means that if we attempt to make use of the INTD interrupt then we're
likely to hit a WARN() in irq_domain_associate() because INTD, or hwirw=4,
is outside of the range covered by the IRQ domain.  irq_domain_associate()
will then return -EINVAL and we'll be unable to make use of INTD.

Fix this by making use of the pci_irqd_intx_xlate() helper function to
translate the 1-4 range used in the DT to a 0-3 range used within the
driver, and stop adding 1 to decoded hwirq numbers.

Whilst cleaning up INTx handling we make use of the new PCI_NUM_INTX macro
& drop the custom INTX definitions.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: "Sören Brinkmann" <soren.brinkmann@xilinx.com>