dt-bindings: virtio: Convert virtio,pci-iommu to DT schema

Convert the binding that describes the virtio-pci based IOMMU to DT
schema. Change the compatible string to "pci<vendor>,<device>", which is
defined by the PCI Bus Binding, but keep "virtio,pci-iommu" as an option
for backward compatibility.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220923074435.420531-1-jean-philippe@linaro.org


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