arm: ls1021aqds: Convert to driver model and enable serial support

Split duart configuration as device tree file. Move /chosen node
out of board commone device tree. Convert ls1021aqds nor and SD
configurations to driver model support (qspi already uses DM).
Enable ns16550 DM serial driver for nor configurations.

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>