PCI: microchip: Move IRQ functions to pcie-plda-host.c

Move IRQ related functions to common file pcie-plda-host.c

The re-use code including MSI, INTx, event interrupts and IRQ init
functions.

Link: https://lore.kernel.org/linux-pci/20240328091835.14797-17-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>

Author: mindachen1987