hw/i386/amd_iommu: Fix device setup failure when PT is on.

hw/i386/amd_iommu: Fix device setup failure when PT is on.

Commit c1f46999ef506 ("amd_iommu: Add support for pass though mode")
introduces the support for "pt" flag by enabling nodma memory when
"pt=off". This allowed VFIO devices to successfully register notifiers
by using nodma region.

But, This also broke things when guest is booted with the iommu=nopt
because, devices bypass the IOMMU and use untranslated addresses (IOVA) to
perform DMA reads/writes to the nodma memory region, ultimately resulting in
a failure to setup the devices in the guest.

Fix the above issue by always enabling the amdvi_dev_as->iommu memory region.
But this will once again cause VFIO devices to fail while registering the
notifiers with AMD IOMMU memory region.

Fixes: c1f46999ef506 ("amd_iommu: Add support for pass though mode")
Signed-off-by: Sairaj Kodilkar <sarunkod@amd.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Message-Id: <20250516100535.4980-2-sarunkod@amd.com>
Fixes: c1f46999ef506 ("amd_iommu: Add support for pass though mode")
Signed-off-by: Sairaj Kodilkar <sarunkod@amd.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>