tty: serial: make SERIAL_SPRD not depend on ARCH_SPRD

Remove the dependency with ARCH_SPRD from sprd serial/console Kconfig-s,
since we want them can be built-in when ARCH_SPRD is set as 'm'.
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Link: https://lore.kernel.org/r/20200305103228.9686-2-zhang.lyra@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/Kconfig

@@ -1443,7 +1443,6 @@ config SERIAL_MEN_Z135
 
 config SERIAL_SPRD
 	tristate "Support for Spreadtrum serial"
-	depends on ARCH_SPRD
 	select SERIAL_CORE
 	help
 	  This enables the driver for the Spreadtrum's serial.