AMD/IOMMU: don't needlessly log headers when dumping IRTs

AMD/IOMMU: don't needlessly log headers when dumping IRTs

Log SBDF headers only when there are actual IRTEs to log. This is
particularly important for the total volume of output when the ACPI
tables describe far more than just the existing devices. On my Rome
system so far there was one line for every function of every device on
all 256 buses of segment 0, with extremely few exceptions (like the
IOMMUs themselves).

Also only log one of the "per-device" or "shared" overall headers.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Brian Woods <brian.woods@amd.com>