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/doc/board/kontron/sl-mx8mm.rst b/doc/board/kontron/sl-mx8mm.rst
index 7a4c113..f022e09 100644
--- a/doc/board/kontron/sl-mx8mm.rst
+++ b/doc/board/kontron/sl-mx8mm.rst
@@ -1,13 +1,16 @@
 .. SPDX-License-Identifier: GPL-2.0+
 
-Kontron Electronics SL i.MX8MM SoM
-==================================
+Kontron Electronics i.MX8MM SoMs and Boards
+===========================================
 
-The Kontron SoM-Line i.MX8MM (N801x) by Kontron Electronics GmbH is a SoM module
+The SL i.MX8MM and OSM-S i.MX8MM by Kontron Electronics GmbH are SoM modules
 with an i.MX8M-Mini SoC, 1/2/4 GB LPDDR4 RAM, SPI NOR, eMMC and PMIC.
 
-The matching evaluation boards (Board-Line) have two Ethernet ports, USB 2.0,
-HDMI/LVDS, SD card, CAN, RS485, RS232 and much more.
+The matching evaluation boards (Board-Line, BL) have two Ethernet ports,
+USB 2.0, HDMI/LVDS, SD card, CAN, RS485, RS232 and much more.
+
+The OSM-S i.MX8MM is compliant to the Open Standard Module (OSM) 1.0
+specification, size S (https://sget.org/standards/osm).
 
 Quick Start
 -----------