arm64: apple: Add PCIe node

Add node corresponding to the apcie,t8103 node in the
Apple device tree for the Mac mini (M1, 2020).

Power domain references and DART (IOMMU) references are left out
at the moment and will be added once the appropriate bindings have
been settled upon.

Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210921183420.436-5-kettenis@openbsd.org
Signed-off-by: Hector Martin <marcan@marcan.st>