LSDK 18.12 is out-of-date - please use LSDK 20.12
LS1043A supports booting from eMMC.
There is no "ls1043ardb_emmc_defconfig" because LS1043ARDB does not possess an eMMC device.
The "ls1043ardb_sdcard_defconfig" and "ls1046ardb_emmc_defconfig" can be used as references for "ls1043ardb_emmc_defconfig".