efi: Update implementation of add_links() to create fwnode links

The semantics of add_links() has changed from creating device link
between devices to creating fwnode links between fwnodes. So, update the
implementation of add_links() to match the new semantics.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20201121020232.908850-16-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>