iommu/amd: Clarify AMD IOMMUv2 initialization messages

The messages printed on the initialization of the AMD IOMMUv2 driver
have caused some confusion in the past. Clarify the messages to lower
the confusion in the future.

Cc: stable@vger.kernel.org
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Link: https://lore.kernel.org/r/20211123105507.7654-3-joro@8bytes.org