arm: ls1021aqds: Enable driver model lpuart serial driver

Convert ls1021aqds_nor_lpuart and ls1021aqds_ddr4_nor_lpuart
to driver model suport. Enable lpuart port driver.

Signed-off-by: York Sun <york.sun@nxp.com>
CC: Alison Wang <alison.wang@nxp.com>
CC: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alison Wang <alison.wang@nxp.com>