configs: imx8mn_bsh_smm_s2: remove console from bootargs

The Linux kernel device tree already specifies the device to be used for
boot console output with a stdout-path property under /chosen.

Co-developed-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>