dt-bindings: PCI: Convert PCIe Host/Endpoint in Cadence platform to DT schema

Include Cadence core DT schema and define the Cadence platform DT schema
for both Host and Endpoint mode. Note: The Cadence core DT schema could
be included for other platforms using Cadence PCIe core.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>