dfu: export dfu_list

This variable will be utilized to enumerate all dfu entities
for UEFI capsule firmware update in a later commit.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

include/dfu.h

@@ -158,6 +158,9 @@ struct dfu_entity {
 	unsigned int inited:1;
 };
 
+struct list_head;
+extern struct list_head dfu_list;
+
 #ifdef CONFIG_SET_DFU_ALT_INFO
 /**
  * set_dfu_alt_info() - set dfu_alt_info environment variable