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.

Commit 36b661dc ("Merge branch 'next'") re-added the console
setting that commit bede82f7 ("configs: imx8mn_bsh_smm_s2: remove
console from bootargs") had previously removed.

Fixes: 36b661dc ("Merge branch 'next'")
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Fabio Estevam <festevam@denx.de>