AMD/IOMMU: return old PTE from {set,clear}_iommu_pte_present()

AMD/IOMMU: return old PTE from {set,clear}_iommu_pte_present()

In order to free intermediate page tables when replacing smaller
mappings by a single larger one callers will need to know the full PTE.
Flush indicators can be derived from this in the callers (and outside
the locked regions). First split set_iommu_pte_present() from
set_iommu_ptes_present(): Only the former needs to return the old PTE,
while the latter (like also set_iommu_pde_present()) doesn't even need
to return flush indicators. Then change return types/values and callers
accordingly.

Note that for subsequent changes returning merely a boolean (old.pr) is
not going to be sufficient; the next_level field will also be required.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>