AMD/IOMMU: don't blindly allocate interrupt remapping tables

AMD/IOMMU: don't blindly allocate interrupt remapping tables

ACPI tables are free to list far more device coordinates than there are
actual devices. By delaying the table allocations for most cases, and
doing them only when an actual device is known to be present at a given
position, overall memory used for the tables goes down from over 500k
pages to just over 1k (on my system having such ACPI table contents).

Tables continue to get allocated right away for special entries
(IO-APIC, HPET) as well as for alias IDs. While in the former case
that's simply because there may not be any device at a given position,
in the latter case this is to avoid having to introduce ref-counting of
table usage.

The change involves invoking
iterate_ivrs_mappings(amd_iommu_setup_device_table) a second time,
because the function now wants to be able to find PCI devices, which
isn't possible yet when IOMMU setup happens very early during x2APIC
mode setup. In this context amd_iommu_init_interrupt() gets renamed as
well.

The logic adjusting a DTE's interrupt remapping attributes also gets
changed, such that the lack of an IRT would result in target aborted
rather than non-remapped interrupts (should any occur).

Note that for now phantom functions get separate IRTs allocated, as was
the case before.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>