efl_ui_bg: fix unclipped image on EFL_UI_IMAGE_SCALE_TYPE_NONE
efl_ui_bg has internal image and image may be larger than
resize_obj when EFL.UI.IMAGE.SCALE_TYPE is none. Now resize_obj clips the internal image.
1.Run elementary_test, part background(will be added soon)
2.Create a bg in a box with other widgets.
Set bg as EFL_UI_IMAGE_SCALYE_TYPE_NONE.
Reviewers: jpeg, cedric
Reviewed By: cedric
Differential Revision: https://phab.enlightenment.org/D5509
Signed-off-by: Cedric Bail <firstname.lastname@example.org>