arm: ls1021a: Adjust memory mapping for Flash/SD card on LS1021AQDS/TWR

This patch is to adjust the memory mapping for FLash/SD card on
LS1021AQDS and LS1021ATWR, such as U-Boot start address on serial
Flash, QE firmware load address and environment address.

Signed-off-by: Alison Wang <alison.wang@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>