ARM: dts: add Plymovent M2M board

Plymovent M2M is a control interface produced for the Plymovent filter
systems.

Co-Developed-by: David Jander <david@protonic.nl>
Signed-off-by: David Jander <david@protonic.nl>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>