Add SD secure boot target for ls1021atwr.
Implement board specific spl_board_init() to setup CAAM stream ID and
corresponding stream ID in SMMU. 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.

Reviewed-by: Aneesh Bansal <aneesh.bansal@nxp.com>
Signed-off-by: Sumit Garg <sumit.garg@nxp.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: York Sun <york.sun@nxp.com>