southbridge: Ensure common Kconfig gets included last

Change-Id: Icaa64e664499090fec3e98687b4827ef27cc201b
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50800
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/Kconfig

@@ -526,6 +526,7 @@ source "src/northbridge/*/*/Kconfig"
 source "src/northbridge/*/*/Kconfig.common"
 comment "Southbridge"
 source "src/southbridge/*/*/Kconfig"
+source "src/southbridge/*/*/Kconfig.common"
 comment "Super I/O"
 source "src/superio/*/*/Kconfig"
 comment "Embedded Controllers"