iommu/vt-d: Split paging_domain_compatible()

Make First/Second stage specific functions that follow the same pattern in
intel_iommu_domain_alloc_first/second_stage() for computing
EOPNOTSUPP. This makes the code easier to understand as if we couldn't
create a domain with the parameters for this IOMMU instance then we
certainly are not compatible with it.

Check superpage support directly against the per-stage cap bits and the
pgsize_bitmap.

Add a note that the force_snooping is read without locking. The locking
needs to cover the compatible check and the add of the device to the list.

Reviewed-by: Kevin Tian <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Lu Baolu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

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