AMD IOMMU: also allocate IRTEs for HPET MSI

AMD IOMMU: also allocate IRTEs for HPET MSI

Omitting this was a blatant oversight of mine in commit 2ca9fbd7 ("AMD
IOMMU: allocate IRTE entries instead of using a static mapping").

This also changes a bogus inequality check into a sensible one, even
though it is already known that this will make HPET MSI unusable on
certain systems (having respective broken firmware). This, however,
seems better than failing on systems with consistent ACPI tables.

Reported-by: Sander Eikelenboom <linux@eikelenboom.it>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>