VT-d: refuse to use IOMMU with reserved CAP.ND value

VT-d: refuse to use IOMMU with reserved CAP.ND value

The field taking the value 7 (resulting in 18-bit DIDs when using the
calculation in cap_ndoms(), when the DID fields are only 16 bits wide)
is reserved. Instead of misbehaving in case we would encounter such an
IOMMU, refuse to use it.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
master commit: a1545fbf45c689aff39ce76a6eaa609d32ef72a7
master date: 2022-04-20 10:54:26 +0200