iommu/arm-smmu-v3: Convert struct device of_node to fwnode usage

Current ARM SMMU v3 driver rely on the struct device.of_node pointer for
device look-up and iommu_ops retrieval.

In preparation for ACPI probing enablement, convert the driver to use
the struct device.fwnode member for device and iommu_ops look-up so that
the driver infrastructure can be used also on systems that do not
associate an of_node pointer to a struct device (eg ACPI), making the
device look-up and iommu_ops retrieval firmware agnostic.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Tomasz Nowicki <tn@semihalf.com>
Tested-by: Hanjun Guo <hanjun.guo@linaro.org>
Tested-by: Tomasz Nowicki <tn@semihalf.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Hanjun Guo <hanjun.guo@linaro.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>