dt-binding: arm/stm32: Add emtrion hardware emSBC-Argon

This patch presents the yaml patch for the emtrion GmbH
Argon board series.

Signed-off-by: Reinhold Mueller <reinhold.mueller@emtrion.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>