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: NVinitha Pillai <vinitha.pillai@nxp.com>
Signed-off-by: NSumit Garg <sumit.garg@nxp.com>
Signed-off-by: NRuchika Gupta <ruchika.gupta@nxp.com>
Reviewed-by: NYork Sun <york.sun@nxp.com>