Hi,
The change to AgcSubmissions.cpp/.h were done to the class FAgcTransientHeapMapper. That class existed in 5.4 in D:\UE_5.4\Engine\Platforms\PS5\Source\Runtime\AgcRHI\Private\AgcContextCommon.cpp. From my quick look, that should be trivial to integrate them as it seems the class was just moved to a different file.
Regards,
Patrick