thermal: exynos: Add the dependency of CONFIG_THERMAL_OF instead of CONFIG_OF

The exynos thermal driver use the of_thermal_*() API to parse the basic data
for thermal management from devicetree file. So, if CONFIG_EXYNOS_THERMAL is
selected without CONFIG_THERMAL_OF, kernel can build it without any problem.
But, exynos thermal driver is not working with following error log. This patch
add the dependency of CONFIG_THERMAL_OF instead of CONFIG_OF.

[ 1.458644] get_th_reg: Cannot get trip points from of-thermal.c!
[ 1.459096] get_th_reg: Cannot get trip points from of-thermal.c!
[ 1.465211] exynos4412_tmu_initialize: No CRITICAL trip point defined at of-thermal.c!

Cc: Zhang Rui <[e-mail]>
Cc: Eduardo Valentin <[e-mail]>
Cc: Lukasz Majewski <[e-mail]>
Signed-off-by: Chanwoo Choi <[e-mail]>
Signed-off-by: Lukasz Majewski <[e-mail]>
Signed-off-by: Eduardo Valentin <[e-mail]>

drivers/thermal/samsung/Kconfig

···
 config EXYNOS_THERMAL
 	tristate "Exynos thermal management unit driver"
-	depends on OF
+	depends on THERMAL_OF
 	help
 	  If you say yes here you get support for the TMU (Thermal Management
 	  Unit) driver for SAMSUNG EXYNOS series of SoCs. This driver initialises