bootstd: Move bootflow-adding to bootstd

This relates to more than just the bootdev, since there is a global list
of bootflows. Move the function to the bootstd file and rename it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/bootflow.c b/cmd/bootflow.c
index f67948d..8962464 100644
--- a/cmd/bootflow.c
+++ b/cmd/bootflow.c
@@ -207,7 +207,7 @@
 		bflow.err = ret;
 		if (!ret)
 			num_valid++;
-		ret = bootdev_add_bootflow(&bflow);
+		ret = bootstd_add_bootflow(&bflow);
 		if (ret) {
 			printf("Out of memory\n");
 			return CMD_RET_FAILURE;