iommu/arm-smmu-v3: Allow ATS for IOMMU_DOMAIN_NESTED

The EATS flag needs to flow through the vSTE and into the pSTE, and ensure
physical ATS is enabled on the PCI device.

The physical ATS state must match the VM's idea of EATS as we rely on the
VM to issue the ATS invalidation commands. Thus ATS must remain off at the
device until EATS on a nesting domain turns it on. Attaching a nesting
domain is the point where the invalidation responsibility transfers to
userspace.

Update the ATS logic to track EATS for nesting domains and flush the
ATC whenever the S2 nesting parent changes.

Link: https://patch.msgid.link/r/11-v4-9e99b76f3518+3a8-smmuv3_nesting_jgg@nvidia.com


Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>