mpc8308: Migrate system io config to Kconfig

Migrate the system IO configuration setting to Kconfig.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
diff --git a/arch/powerpc/cpu/mpc83xx/Kconfig b/arch/powerpc/cpu/mpc83xx/Kconfig
index 9637683..9f7b3a2 100644
--- a/arch/powerpc/cpu/mpc83xx/Kconfig
+++ b/arch/powerpc/cpu/mpc83xx/Kconfig
@@ -294,6 +294,7 @@
 source "arch/powerpc/cpu/mpc83xx/lblaw/Kconfig"
 source "arch/powerpc/cpu/mpc83xx/elbc/Kconfig"
 source "arch/powerpc/cpu/mpc83xx/hid/Kconfig"
+source "arch/powerpc/cpu/mpc83xx/sysio/Kconfig"
 
 menu "Legacy options"