dt-bindings: net: qcom,ethqos: Convert bindings to yaml

Convert Qualcomm ETHQOS Ethernet devicetree binding to YAML.
In doing so add a new property for iommus since newer platforms support
using one, and without such make dtbs_check fails on them.

While at it, also update the MAINTAINERS file to point to the yaml
version of the bindings.

Signed-off-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>
[halaney: Remove duplicated properties, add MAINTAINERS and iommus]
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
Tested-by: Brian Masney <bmasney@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>