dt-bindings: PCI: Add Intel Keem Bay PCIe controller

Document DT bindings for PCIe controller found on Intel Keem Bay SoC.

Link: https://lore.kernel.org/r/20210805211010.29484-2-srikanth.thokala@intel.com


Signed-off-by: Wan Ahmad Zainie <wan.ahmad.zainie.wan.mohamad@intel.com>
Signed-off-by: Srikanth Thokala <srikanth.thokala@intel.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>