ANDROID: KVM: arm64: iommu: Snapshot host stage-2

Snapshot the host stage-2 in the idmapped domain, this is done
differently from the Android14:

- Instead of assuming that the page table maps all the memory and
  the snapshot function would only unmap the donated pages, now the
  polarity is the opposite, where the page table is assumed to be
  empty and the snapshot function would map all host memory, so this
  slower, but done only once at boot, and that won't require the
  module to know the memory map.

- Instead of calling snapshot at init, now it is exported to modules,
  as some IOMMUs as SMMUv3 doens't know the format of the page table
  until the device is attached.

Bug: 277989609
Bug: 278749606
Change-Id: I82dbf273eebc4e5c588c230a3a9bb18ef7b468ea
Signed-off-by: Mostafa Saleh <smostafa@google.com>