iommu/amd: Move Stoney Ridge check to detect_ivrs()

The AMD IOMMU will not be enabled on AMD Stoney Ridge systems. Bail
out even earlier and refuse to even detect the IOMMU there.

References: https://bugzilla.kernel.org/show_bug.cgi?id=212133
References: https://bugzilla.suse.com/show_bug.cgi?id=1183132


Cc: stable@vger.kernel.org # v5.11
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Link: https://lore.kernel.org/r/20210317091037.31374-2-joro@8bytes.org


Acked-by: Huang Rui <ray.huang@amd.com>