powerpc/mpc85xx: SECURE BOOT- Enable chain of trust in SPL

As part of Chain of Trust for Secure boot, the SPL U-Boot will validate
the next level U-boot image. Add a new function spl_validate_uboot to
perform the validation.

Enable hardware crypto operations in SPL using SEC block.
In case of Secure Boot, PAMU is not bypassed. For allowing SEC block
access to CPC configured as SRAM, configure PAMU.

Reviewed-by: Ruchika Gupta <ruchika.gupta@nxp.com>
Signed-off-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>