MdePkg: Rename SBSA Generic Watchdog to Arm Generic Watchdog

MdePkg: Rename SBSA Generic Watchdog to Arm Generic Watchdog

Bugzilla: 3516 (https://bugzilla.tianocore.org/show_bug.cgi?id=3516)

Make changes to ACPI 6.4 header according to the latest specification:
- ACPI 6.4 January 2021, Section 5.2.24, Table 5.100 & Section 5.2.24.2
- Mantis ID 2126 (https://mantis.uefi.org/mantis/view.php?id=2126)

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>