ARM: exynos_defconfig: Enable CONFIG_SENSORS_PWM_FAN for Odroid-XU3

Enable CONFIG_SENSORS_PWM_FAN on exynos_defconfig to control fan
power on Odroid-XU3.

Signed-off-by: Anand Moon <linux.amoon@gmail.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>