Change the confuse "VFIO IOMMU check failed" error message by
the explicit "VFIO IOMMU Type1 is not supported" once.

Example on POWER:

 $ qemu-system-ppc64 -drive if=none,id=nvme0,file=nvme://0001:01:00.0/1,format=raw
 qemu-system-ppc64: -drive if=none,id=nvme0,file=nvme://0001:01:00.0/1,format=raw: VFIO IOMMU Type1 is not supported

Suggested-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Fam Zheng <fam@euphon.net>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20201103020733.2303148-2-philmd@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>