For both SoCs data found in SBMR registers reflects only the boot
source that was selected via pins of fuses and not the final boot
source that ended up being used by MaskROM code. Original i.MX7 boot
source detection implementation worked around that fact by having a
special code to correctly handle "Manufacturing Mode".

MaskROM in i.MX8MQ changed what SoC uses as recovery device and
switched it to be USDHC2. It also made recovery device switch always
enabled. Since correct actual boot source detection is important to
being able to properly boot i.MX8MQ (due to not using DCD to
initialize RAM), change the code to handle described exception.

Instead of trying to adapt original i.MX7 code with yet another
special case if(), change the whole thing to do what U-Boot does on
i.MX7 and i.MX8MQ and use "Boot information for software" provided by
recent (found in i.MX7 and i.MX8MQ) versions of MaskROM.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>