kconfig: remove meaningless prefixes in defconfig files

Since commit e02ee2548afe (kconfig: switch to single .config
configuration), the prefixes in defconfig files such as "+S:",
"+ST:", etc., are meaningless.

This commit was generated by the following command:

  find configs -name '*_defconfig' | xargs sed -i 's/^+*S*T*://'

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/configs/mx23evk_defconfig b/configs/mx23evk_defconfig
index 963cec3..a2d2891 100644
--- a/configs/mx23evk_defconfig
+++ b/configs/mx23evk_defconfig
@@ -1,3 +1,3 @@
 CONFIG_SPL=y
-+S:CONFIG_ARM=y
-+S:CONFIG_TARGET_MX23EVK=y
+CONFIG_ARM=y
+CONFIG_TARGET_MX23EVK=y