ARM: imx: Add support for detecting primary/secondary bmode on MX8M

Implement the 'getprisec' subcommand of 'bmode' command for i.MX8M by
reading out the ROM log events. This event is set by the BootROM if it
switched to the secondary copy due to primary copy being corrupted.

Signed-off-by: Fedor Ross <fedor.ross@ifm.com>
Signed-off-by: Marek Vasut <marex@denx.de>