MdePkg: Add Generic Initiator Affinity Structure definitions to SRAT

MdePkg: Add Generic Initiator Affinity Structure definitions to SRAT

Add Generic Initiator Affinity Structure to the list of recognised
System Resource Affinity Table (SRAT) structure types.

Add definitions for Device Handle Types inside the Generic Initiator
Affinity Structure.

References:
- ACPI 6.3 January 2019, Table 5-78

Signed-off-by: Krzysztof Koch <krzysztof.koch@arm.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Alexei Fedorov <Alexei.Fedorov@arm.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>