uboot-imx

MLK-20553-1 doc: imx: ahab: Add AHAB introduction

The AHAB is currently supported in i.MX8QXP and i.MX8QM devices.

Add an introductory document containing the following topics:

- AHAB Secure Boot Architecture
- System Control Unit (SCU) introduction
- Security Controller (SECO) introduction
- i.MX8/8x secure boot flow
- AHAB PKI tree generation
- SRK Table and SRK Hash generation

Signed-off-by: Breno Lima <breno.lima@nxp.com>
Reviewed-by: Frank Zhang <frank.zhang@nxp.com>
Reviewed-by: Marius Grigoras <marius.grigoras@nxp.com>
Reviewed-by: Utkarsh Gupta <utkarsh.gupta@nxp.com>
(cherry picked from commit 6e9ceb2526bd4a45c6ff669afb086cc3a0627e6b)