High Assurance Boot (HAB) for i.MX6 CPUs

To authenticate U-Boot only by the CPU there is no code required in
U-Boot itself. However, the U-Boot image to be programmed into the
boot media needs to be properly constructed, i.e. it must contain a
proper Command Sequence File (CSF).

The Initial Vector Table contains a pointer to the CSF. Please see
doc/README.imximage for how to prepare u-boot.imx.

The CSF itself is being generated by Freescale HAB tools.

mkimage will output additional information about "HAB Blocks"
which can be used in the Freescale tooling to authenticate U-Boot
(entries in the CSF file).

Image Type:   Freescale IMX Boot Image
Image Ver:    2 (i.MX53/6 compatible)
Data Size:    327680 Bytes = 320.00 kB = 0.31 MB
Load Address: 177ff420
Entry Point:  17800000
HAB Blocks:   177ff400 00000000 0004dc00
	      ^^^^^^^^ ^^^^^^^^ ^^^^^^^^
		|	|	   |
		|	|	   -------- (1)
		|	|
		|	------------------- (2)
		|
		--------------------------- (3)

(1)	Size of area in file u-boot.imx to sign
	This area should include the IVT, the Boot Data the DCD
	and U-Boot itself.
(2)	Start of area in u-boot.imx to sign
(3)	Start of area in RAM to authenticate

CONFIG_SECURE_BOOT currently enables only an additional command
'hab_status' in U-Boot to retrieve the HAB status and events. This
can be useful while developing and testing HAB.

Commands to generate a signed U-Boot using Freescale HAB tools:
cst --o U-Boot_CSF.bin < U-Boot.CSF
objcopy -I binary -O binary --pad-to 0x2000 --gap-fill=0x00 \
	U-Boot_CSF.bin U-Boot_CSF_pad.bin
cat u-boot.imx U-Boot_CSF_pad.bin > u-boot-signed.imx

NOTE: When booting from NAND, the u-boot image must be padded to the
size indicated in the Boot Data size field. The padding must be
added to the end of the file, after any U-Boot_CSF.bin.
