If you have purchased CodeWarrior license, you could install CodeWarrior for ARMv8 11.5.12 to do your custom board bringing up.
Please sign in www.nxp.com, you can download CodeWarrior for ARMv8 11.5.12 from "My NXP Account->Software Licensing and Support->View accounts->NXP Software->CodeWarrior Networked Suite -Specialist Level->11.5.12 CodeWarrior for QorIQ LS Series ARMv8 ISA".
Please download and install CodeWarrior for ARMv8 v11.5.0 b200629 first, then open CodeWarrior IDE and install service pack 11.5.12 from Help->Install New Software->Add->Archive.
Please refer to C:\Freescale\CW4NET_v2020.06\CW_ARMv8\ARMv8\Help\PDFARMv8_Targeting_Manual.pdf
You also could refer to LSDK 21.08 which supports LS1043ARDB, you could modify atf and u-boot source code according to your custom board based on the source code for LS1043ARDB.
I attached LSDK 21.08 and its user guide to you.
