feat(drtm): add ACPI table region size to the DLME header

The DRTM 1.0 spec defines an additional field in the DLME
header for an optional region in the DLME to hold ACPI tables.

Signed-off-by: Stuart Yoder <stuart.yoder@arm.com>
Change-Id: Idba7fa6bd0fb4ef2bdffc24f4588720e1661e58c