conf: Simplify IOMMU device validation
conf: Simplify IOMMU device validation

Instead of duplicating the list of attributes that are not
allowed for some of the IOMMU models, use two separate switch
statements: one for the attributes and one for the address.

Signed-off-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>
Reviewed-by: Pavel Hrdina <d4772d05997b8abf035041e3b4f4996380ea7e7a@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

jfehlig/libvirt,zippy2/libvirt,olafhering/libvirt,olafhering/libvirt,libvirt/libvirt,zippy2/libvirt,jfehlig/libvirt,zippy2/libvirt,jfehlig/libvirt,olafhering/libvirt,libvirt/libvirt,jfehlig/libvirt,olafhering/libvirt,libvirt/libvirt,libvirt/libvirt,zippy2/libvirt