From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
The updates of the PTEs in the nested page table will be propagated to the
hardware caches on both IOMMU (IOTLB) and devices (DevTLB/ATC).
Add a new domain op cache_invalidate_user for the userspace to flush the
hardware caches for a nested domain through iommufd. No wrapper for it,
as it's only supposed to be used by iommufd. Then, pass in invalidation
requests in form of a user data array conatining a number of invalidation
data entries.