PCI: microchip: Add request_event_irq() callback function

PCI: microchip: Add request_event_irq() callback function

As the PLDA DT binding doc (Documentation/devicetree/bindings/pci/
plda,xpressrich3-axi-common.yaml) shows, the PLDA IP contains an interrupt
controller. Microchip PolarFire add some interrupts based on PLDA interrupt
controller.

The Microchip PolarFire PCIe additional interrupts (defined in
drivers/pci/controller/plda/pcie-microchip-host.c):

  EVENT_PCIE_L2_EXIT
  EVENT_PCIE_HOTRST_EXIT
  EVENT_PCIE_DLUP_EXIT
  EVENT_SEC_TX_RAM_SEC_ERR
  EVENT_SEC_RX_RAM_SEC_ERR
  ...

Both event_cause[] and mc_event_handler() contain additional interrupt
symbol names; these can not be re-used. Add a new plda_event_handler()
function, which implements PLDA interrupt defalt handler, and add a
request_event_irq() callback function for Microchip PolarFire additional
interrupts.

[kwilczynski, bhelgaas: commit log]
Link: https://lore.kernel.org/linux-pci/20240328091835.14797-13-minda.chen@starfivetech.com
Signed-off-by: Minda Chen <minda.chen@starfivetech.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>