dm: exynos: Correct CONFIG_SYS_BOARD setting for Odroid XU3 boards

dm: exynos: Correct CONFIG_SYS_BOARD setting for Odroid XU3 boards

Fix the issue where CONFIG_SYS_BOARD was incorrectly set on
Odroid XU3 boards, causing boot failure. This was resolved by
correcting the SYS_BOARD entry in Kconfig to load the correct
device tree source (dts) for the Odroid Exynos5422 Platforms.

Fixes: f76750d11133 ("Convert CONFIG_CONS_INDEX et al to Kconfig")
Signed-off-by: Anand Moon <linux.amoon@gmail.com>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>