imx: imx_hab: Define a HAB header file

imx: imx_hab: Define a HAB header file

The High Assurance Boot or HAB is an on-chip method of providing a
root-of-trust from the reset vector to subsequent stages in the bootup
flow of the Cortex-A7 on the i.MX series of processors.

This patch adds a simple header file with pointer offsets of the provided
set of HAH API callbacks in the BootROM.

The relative offset of the function pointers is a constant and known
quantum, a software-contract between NXP and an implementation which is
defined in the NXP HAB documentation.

All we need is the correct base offset and then we can map the set of
function pointers relative to that offset.

imx_hab_arch.h provides the correct offset and the imx_hab.h hooks the
offset to the pre-determined callbacks.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Ryan Harkin <ryan.harkin@linaro.org>