dt-bindings: arm: ti: Add bindings for PHYTEC AM64x based hardware

Add devicetree bindings for AM64x based phyCORE-AM64 SoM
and phyBOARD-Electra RDK.

Signed-off-by: Wadim Egorov <w.egorov@phytec.de>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20230104162927.1215033-1-w.egorov@phytec.de