LS1021ATWR: Modify u-boot size for sd secure boot

LS1021ATWR: Modify u-boot size for sd secure boot

Raw uboot image is used in place of FIT image in secure boot.
The maximum allocated size of raw u-boot bin is 1MB in memory map.
Hence , CONFIG_SYS_MONITOR_LEN has been modified to 1 MB.
The bootscript  (BS_ADDR) and its header (BS_HDR_ADDR) offset on
MMC have also been modified to accommodate the increase in uboot size.

Signed-off-by: Vinitha Pillai-B57223 <vinitha.pillai@nxp.com>
Reviewed-by: Sumit Garg <sumit.garg@nxp.com>
Reviewed-by: Ruchika Gupta <ruchika.gupta@nxp.com>
Reviewed-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>