hw/arm/virt-acpi-build: Fix id_count in build_iort_id_mapping

hw/arm/virt-acpi-build: Fix id_count in build_iort_id_mapping

It's observed that Linux kernel booting with the VM reports a "conflicting
mapping for input ID" FW_BUG.

The IORT doc defines "Number of IDs" to be "the number of IDs in the range
minus one", while virt-acpi-build.c simply stores the number of IDs in the
id_count without the "minus one". Meanwhile, some of the callers pass in a
0xFFFF following the spec. So, this is a mismatch between the function and
its callers.

Fix build_iort_id_mapping() by internally subtracting one from the pass-in
@id_count. Accordingly make sure that all existing callers pass in a value
without the "minus one", i.e. change all 0xFFFFs to 0x10000s.

Also, add a few lines of comments to highlight this change along with the
referencing document for this build_iort_id_mapping().

Fixes: 42e0f050e3a5 ("hw/arm/virt-acpi-build: Add IORT support to bypass SMMUv3")
Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Message-Id: <20240619201243.936819-1-nicolinc@nvidia.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>