intel_iommu: convert dbg macros to traces for inv

VT-d codes are still using static DEBUG_INTEL_IOMMU macro. That's not
good, and we should end the day when we need to recompile the code
before getting useful debugging information for vt-d. Time to switch to
the trace system. This is the first patch to do it.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>