Make changes to ACPI 6.4 header according to the latest specification:
- ACPI 6.4 January 2021, Section 5.2.26.1.1
- Mantis ID 2111 (https://mantis.uefi.org/mantis/view.php?id=2111)
Signed-off-by: Chris Jones <christopher.jones@arm.com> Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn> Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>