dt-bindings: PCI: Add SiFive FU740 PCIe host controller

Add PCIe host controller DT bindings of SiFive FU740.

Link: https://lore.kernel.org/r/20210504105940.100004-5-greentime.hu@sifive.com


Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>