You could download LSDK 21.08 pre-built firmware image with the following command.
wget https://www.nxp.com/lgfiles/sdk/lsdk2108/firmware_ls1046ardb_qspiboot.img
Then deploy it on the alternate bank of QSPI flash on the target board.
=>tftp 0xa0000000 firmware_ls1046ardb_qspiboot.img
=>sf probe 0:1
=> sf erase 0 +$filesize
=>sf write 0xa0000000 0 $filesize