For validating images from uboot (Such as Kernel Image), either keys
from SoC fuses can be used or keys from a verified table of public
keys can be used. The latter feature is called IE Key Extension
Feature.

For Layerscape Chasis 3 based platforms, IE table is validated by
Bootrom and address of this table is written in scratch registers 13
and 14 via PBI commands.

Following are the steps describing usage of this feature:

1) Verify IE Table in ISBC phase using keys stored in fuses.
2) Install IE table. (To be used across verification of multiple
   images stored in a static global structure.)
3) Use keys from IE table, to verify further images.

Signed-off-by: Aneesh Bansal <aneesh.bansal@nxp.com>
Signed-off-by: Saksham Jain <saksham.jain@nxp.com>
Signed-off-by: Udit Agarwal <udit.agarwal@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>