iommu: add IOMMU_EXEC flag for safely allowing XN mappings
iommu: add IOMMU_EXEC flag for safely allowing XN mappings

Whilst most IOMMU mappings should probably be non-executable, there
may be cases (HSA?) where executable mappings are required.

This patch introduces a new mapping flag, IOMMU_EXEC, to indicate that
the mapping should be mapped as executable.

Signed-off-by: Will Deacon <b913f13ef92ac157955c954ccaaff7be065faba4@arm.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs