dt-bindings: PCI: mediatek: Add Airoha EN7532 support

Add a binding for Airoha EN7532, an ARM-based platform SoC integrating the
same PCIe IP as MT7622.

Link: https://lore.kernel.org/r/20220615125335.96089-1-nbd@nbd.name


Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rob Herring <robh@kernel.org>