Add PLDA XpressRICH PCIe host common properties dt-binding doc.

The PolarFire PCIe host uses PLDA IP. Move common properties from Microchip
PolarFire PCIe host to PLDA files.

Link: https://lore.kernel.org/linux-pci/20240328091835.14797-2-minda.chen@starfivetech.comSigned-off-by: Minda Chen <minda.chen@starfivetech.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
[bhelgaas: adapt for 5db62b7d ("dt-bindings: PCI: host-bridges: Switch
from deprecated pci-bus.yaml")]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Hal Feng <hal.feng@starfivetech.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Tested-by: John Clark <inindev@gmail.com>