doc: Move UEFI under develop/

Much of the content here is useful only for development. Move it under
that section.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/doc/develop/index.rst b/doc/develop/index.rst
index 41c0ba1..84914bb 100644
--- a/doc/develop/index.rst
+++ b/doc/develop/index.rst
@@ -13,6 +13,7 @@
    global_data
    logging
    menus
+   uefi/index
    version
 
 Debugging