dt-bindings: soc: add samsung,boot-mode definitions

Adds samsung,boot-mode.h header file which contains boot mode
definitions for bootloader. As for now, there are only boot mode
definitions for Exynos Auto v9 SoC.

Signed-off-by: Chanho Park <chanho61.park@samsung.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220523121244.67341-2-chanho61.park@samsung.com
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>