dt-bindings: pci: Add DT bindings for apple,pcie

The Apple PCIe host controller is a PCIe host controller with
multiple root ports present in Apple ARM SoC platforms, including
various iPhone and iPad devices and the "Apple Silicon" Macs.

Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
Link: https://lore.kernel.org/r/20210921183420.436-4-kettenis@openbsd.org


Signed-off-by: Rob Herring <robh@kernel.org>