dt-bindings: PCI: microchip: Add Microchip PolarFire host binding

Add device tree bindings for the Microchip PolarFire PCIe controller
when configured in host (Root Complex) mode.

Link: https://lore.kernel.org/r/20210125162934.5335-3-daire.mcnamara@microchip.com


Signed-off-by: Daire McNamara <daire.mcnamara@microchip.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rob Herring <robh@kernel.org>