dt-bindings: arm: ti: Add bindings for Siemens IOT2050 PG2 boards

Product Generation 2 (PG2) boards are based on SR2.x SoCs and will be
released soon.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/5d99e69ff1e2fb78f51f03c351eff1fe1f6c3a71.1632657917.git.jan.kiszka@web.de