bootz: un-staticize do_bootz

Make do_bootz available for other functions like do_bootm is.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
diff --git a/common/cmd_bootm.c b/common/cmd_bootm.c
index 05130b6..e452fca 100644
--- a/common/cmd_bootm.c
+++ b/common/cmd_bootm.c
@@ -1707,7 +1707,7 @@
 	return 0;
 }
 
-static int do_bootz(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
+int do_bootz(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	bootm_headers_t	images;