arm: ls1043ardb: Add NAND secure boot target

Add NAND secure boot target for ls1043ardb.

- Change the u-boot size defined by a macro for copying the main
  U-Boot by SPL to also include the u-boot Secure Boot header size as
  header is appended to u-boot image. So header will also be copied
  from SD to DDR.
- MACRO for CONFIG_BOOTSCRIPT_COPY_RAM is enabled to copy Bootscript
  from NAND to DDR. Offsets for Bootscript on NAND and DDR have been
  also defined.

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