iommu/arm-smmu-v3: Move definitions to a header

Allow sharing structure definitions with the upcoming SVA support for
Arm SMMUv3, by moving them to a separate header. We could surgically
extract only what is needed but keeping all definitions in one place
looks nicer.
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/20200918101852.582559-8-jean-philippe@linaro.orgSigned-off-by: Will Deacon <will@kernel.org>