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>

include/bootdev.h

@@ -195,21 +195,6 @@ void bootdev_list(bool probe);
  */
 void bootdev_clear_bootflows(struct udevice *dev);
 
-/**
- * bootdev_add_bootflow() - Add a bootflow to the bootdev's list
- *
- * All fields in @bflow must be set up. Note that @bflow->dev is used to add the
- * bootflow to that device.
- *
- * @dev: Bootdev device to add to
- * @bflow: Bootflow to add. Note that fields within bflow must be allocated
- *	since this function takes over ownership of these. This functions makes
- *	a copy of @bflow itself (without allocating its fields again), so the
- *	caller must dispose of the memory used by the @bflow pointer itself
- * Return: 0 if OK, -ENOMEM if out of memory
- */
-int bootdev_add_bootflow(struct bootflow *bflow);
-
 /**
  * bootdev_first_bootflow() - Get the first bootflow from a bootdev
  *