dt-bindings: PCI: Add Amazon's Annapurna Labs PCIe host bridge binding

Document Amazon's Annapurna Labs PCIe host bridge.

Signed-off-by: Jonathan Chocron <jonnyc@amazon.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>