arm64: dts: Add support for Kontron SL/BL i.MX8MM OSM-S

This adds support for the Kontron Electronics SL i.MX8MM OSM-S SoM
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

).

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>