thermal: offer Samsung thermal support only when ARCH_EXYNOS is defined

Menu for Samsung thermal support is visible on all Samsung
platforms while thermal drivers are currently available only
for EXYNOS SoCs. Fix it by replacing PLAT_SAMSUNG dependency
with ARCH_EXYNOS one.
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>

drivers/thermal/Kconfig

@@ -227,7 +227,7 @@ source "drivers/thermal/ti-soc-thermal/Kconfig"
 endmenu
 
 menu "Samsung thermal drivers"
-depends on PLAT_SAMSUNG
+depends on ARCH_EXYNOS
 source "drivers/thermal/samsung/Kconfig"
 endmenu