dt-bindings: PCI: qcom: Allow 'dma-coherent' property

Devices on some PCIe buses may be cache coherent and must be marked as
such in the devicetree to avoid data corruption.

This is specifically needed on recent Qualcomm platforms like SC8280XP.

Link: https://lore.kernel.org/r/20221205094530.12883-1-johan+linaro@kernel.org


Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>