imx: kontron-sl-mx8mm: Enable bootaux command

Enable the bootaux command in order to be able to load a
binary into the M4 core when needed.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Fabio Estevam <festevam@denx.de>
diff --git a/configs/kontron-sl-mx8mm_defconfig b/configs/kontron-sl-mx8mm_defconfig
index 18b926e..fe29866 100644
--- a/configs/kontron-sl-mx8mm_defconfig
+++ b/configs/kontron-sl-mx8mm_defconfig
@@ -22,6 +22,7 @@
 CONFIG_ENV_OFFSET_REDUND=0x1F0000
 CONFIG_SPL_SPI_FLASH_SUPPORT=y
 CONFIG_SPL_SPI=y
+CONFIG_IMX_BOOTAUX=y
 CONFIG_SYS_LOAD_ADDR=0x42000000
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_FIT=y