scripts: imx-image: super_root_key command depends on header_version 1
The Super Root Key pointer exclusively exists in flash header version 1
which is used for i.MX25, i.MX35 and i.MX51 SOC as described in freescales
AN4547 document. Simplify the code a little bit.
Signed-off-by: Alexander Kurz <akurz@blala.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>