bootz: un-staticize do_bootz

bootz is needed for sysboot command.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
diff --git a/common/cmd_bootm.c b/common/cmd_bootm.c
index d256ddf..717e9a8 100644
--- a/common/cmd_bootm.c
+++ b/common/cmd_bootm.c
@@ -1601,7 +1601,7 @@
 	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;