dt-bindings: PCI: microchip,pcie-host: fix missing clocks properties

Recent versions of dt-schema warn about unevaluatedProperties:
arch/riscv/boot/dts/microchip/mpfs-icicle-kit.dtb: pcie@2000000000: Unevaluated properties are not allowed ('clock-names', 'clocks', 'legacy-interrupt-controller', 'microchip,axi-m-atr0' were unexpected)
        From schema: Documentation/devicetree/bindings/pci/microchip,pcie-host.yaml

The clocks are required to enable interfaces between the FPGA fabric
and the core complex, so add them to the binding.

Link: https://lore.kernel.org/r/20220819231415.3860210-3-mail@conchuod.ie


Fixes: 6ee6c89a ("dt-bindings: PCI: microchip: Add Microchip PolarFire host binding")
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>