ACPI: HMAT: Fix handling of changes from ACPI 6.2 to ACPI 6.3

In ACPI 6.3, the Memory Proximity Domain Attributes Structure
changed substantially.  One of those changes was that the flag
for "Memory Proximity Domain field is valid" was deprecated.

This was because the field "Proximity Domain for the Memory"
became a required field and hence having a validity flag makes
no sense.

So the correct logic is to always assume the field is there.
Current code assumes it never is.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>