Platform/ARM/SgiPkg: Let platform specify the ACPI tables to include

The last change in moving away from single binary for all SGI/RD
platforms to independent binary for each platform is to let the platform
select only the ACPI table module that is required for the platform.

Each platform dsc file specifies the ACPI table module to use. All the
platform specific ACPI table modules are assigned a common file guid
which is looked up by the platform dxe driver, thereby, removing the
need to lookup for a ACPI table module file guid using the platform
id hob.

Signed-off-by: Aditya Angadi <aditya.angadi@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>