distro: Enable iso partition code

Now that we can properly boot EFI payloads from iso el torito
images, let's enable support for isos by default in the distro
header.

Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/include/config_distro_defaults.h b/include/config_distro_defaults.h
index 2ba7cf4..076be4d 100644
--- a/include/config_distro_defaults.h
+++ b/include/config_distro_defaults.h
@@ -62,6 +62,7 @@
 #define CONFIG_MENU
 #define CONFIG_DOS_PARTITION
 #define CONFIG_EFI_PARTITION
+#define CONFIG_ISO_PARTITION
 #define CONFIG_SUPPORT_RAW_INITRD
 #define CONFIG_SYS_HUSH_PARSER