imx: kontron-sl-mx8mm: Prepare for other i.MX8MM SoM types

This sets an env variable 'som_type' from the board code. It can
later be used by environment scripts, e. g. to select the proper
devicetree for the board.

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 fe29866..f273f22 100644
--- a/configs/kontron-sl-mx8mm_defconfig
+++ b/configs/kontron-sl-mx8mm_defconfig
@@ -31,6 +31,7 @@
 # CONFIG_USE_SPL_FIT_GENERATOR is not set
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_BOARD_TYPES=y
+CONFIG_BOARD_LATE_INIT=y
 CONFIG_SPL_HAS_BSS_LINKER_SECTION=y
 CONFIG_SPL_BSS_START_ADDR=0x910000
 CONFIG_SPL_BSS_MAX_SIZE=0x2000