Please refer to packages/firmware/atf/plat/nxp/soc-ls1046/ls1046ardb/ddr_init.c in LSDK, did you also use reading DDR controller configuration parameters form SPD?
Please check whether "define NXP_SPD_EEPROM0 0x51" defined in atf/plat/nxp/soc-ls1046/ls1046ardb/platform_def.h is suitable for your custom board.