Secure boot with HAB requires handling of the super root key hash
and actually locking down the device. The related information is
stored in the i.MX fusebox device (IIM on older SoCs, OCOTP on newer
SoCs). This patch adds several convenience functions to store and
read the super root key hash and to lock down a SoC. Also we add
a command to do this from the command line.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>