HMAT: Skip publishing target info for nodes with no online memory

There are multiple scenarios where the HMAT may contain information
about proximity domains that are not currently online. Rather than fail
to report any HMAT data just elide those offline domains.

If and when those domains are later onlined they can be added to the
HMEM reporting at that point.

This was found while testing EFI_MEMORY_SP support which reserves
"specific purpose" memory from the general allocation pool. If that
reservation results in an empty numa-node then the node is not marked
online leading a spurious:

    "acpi/hmat: Ignoring HMAT: Invalid table"

...result for HMAT parsing.

Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>