ls102xa: Adjust some macros for SD boot on LS1021A QDS board

ls102xa: Adjust some macros for SD boot on LS1021A QDS board

As more features are added for SD boot on LS1021A QDS board,
the size of U-Boot is larger. CONFIG_SYS_U_BOOT_MAX_SIZE_SECTORS
needs to be adjusted to a suitable value.

Starting address of the malloc pool used in SPL needs to be
adjusted too, or it will occupy the address u-boot loads.

Signed-off-by: Alison Wang <alison.wang@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>