dt-bindings: arm: ti: Add binding for AM69 Starter Kit

AM69 Starter Kit is a single board designed for TI AM69 SoC.
The AM69 SoC belongs to the K3 Multicore SoC architecture platform,
providing advanced system integration in automotive ADAS applications,
autonomous mobile robot and edge AI applications.

Add DT binding for AM69 Starter Kit.

Signed-off-by: Dasnavis Sabiya <sabiya.d@ti.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20230119132958.124435-2-sabiya.d@ti.com