Revert "tty: serial: samsung_tty: build it for any platform"

This reverts commit 175b558d.

When the user configures a kernel without support for Samsung SoCs, it
makes no sense to ask the user about enabling "Samsung SoC serial
support", as Samsung serial ports can only be found on Samsung SoCs.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200306102301.16870-1-geert+renesas@glider.beSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/Kconfig

@@ -237,6 +237,7 @@ config SERIAL_CLPS711X_CONSOLE
 
 config SERIAL_SAMSUNG
 	tristate "Samsung SoC serial support"
+	depends on PLAT_SAMSUNG || ARCH_EXYNOS || COMPILE_TEST
 	select SERIAL_CORE
 	help
 	  Support for the on-chip UARTs on the Samsung S3C24XX series CPUs,