imx: kontron-sl-mx8mm: Add support for Kontron Electronics SoM SL i.MX8MM OSM-S

This adds support for the Kontron Electronics SoM SL i.MX8MM OSM-S
and the matching baseboard BL i.MX8MM OSM-S.

The SoM hardware complies to the Open Standard Module (OSM) 1.0
specification, size S (https://sget.org/standards/osm).

The existing board configuration for the non-OSM SoM is reused and
allows to detect the SoM variant at runtime.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Fabio Estevam <festevam@denx.de>
diff --git a/board/kontron/sl-mx8mm/sl-mx8mm.c b/board/kontron/sl-mx8mm/sl-mx8mm.c
index 6e73ede..6411301 100644
--- a/board/kontron/sl-mx8mm/sl-mx8mm.c
+++ b/board/kontron/sl-mx8mm/sl-mx8mm.c
@@ -123,7 +123,12 @@
 
 int board_late_init(void)
 {
-	env_set("som_type", "sl");
+	if (!fdt_node_check_compatible(gd->fdt_blob, 0, "kontron,imx8mm-n802x-som") ||
+	    !fdt_node_check_compatible(gd->fdt_blob, 0, "kontron,imx8mm-osm-s")) {
+		env_set("som_type", "osm-s");
+	else
+		env_set("som_type", "sl");
+
 	return 0;
 }