i.MX8 only support AHAB secure boot with Container format image,
we could not use FIT to support secure boot, so introduce container
support to let SPL could load container images.

Cc: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Cc: Tien Fong Chee <tien.fong.chee@intel.com>
Cc: York Sun <york.sun@nxp.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Alex Kiernan <alex.kiernan@gmail.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Cc: Kever Yang <kever.yang@rock-chips.com>
Cc: Heiko Schocher <hs@denx.de>
Signed-off-by: NPeng Fan <peng.fan@nxp.com>