tty: serial: Make the STM32 serial port depend on it's arch

The STM32 serial port is SoC specific so no point enabling it
without the architecture enabled.
Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/Kconfig

@@ -1639,7 +1639,7 @@ config SERIAL_STM32
 	tristate "STMicroelectronics STM32 serial port support"
 	select SERIAL_CORE
 	depends on HAS_DMA
-	depends on ARM || COMPILE_TEST
+	depends on ARCH_STM32 || COMPILE_TEST
 	help
 	  This driver is for the on-chip Serial Controller on
 	  STMicroelectronics STM32 MCUs.