kconfig: add CONFIG_SUPPORT_SPL

CONFIG_SPL should not be enabled for boards that do not have SPL.
CONFIG_SUPPORT_SPL introduced by this commit should be "select"ed
by boards with SPL support and CONFIG_SPL should depend on it.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/powerpc/cpu/mpc83xx/Kconfig b/arch/powerpc/cpu/mpc83xx/Kconfig
index 42e0e29..2a1abe0 100644
--- a/arch/powerpc/cpu/mpc83xx/Kconfig
+++ b/arch/powerpc/cpu/mpc83xx/Kconfig
@@ -24,6 +24,7 @@
 
 config TARGET_MPC8313ERDB
 	bool "Support MPC8313ERDB"
+	select SUPPORT_SPL
 
 config TARGET_MPC8315ERDB
 	bool "Support MPC8315ERDB"