evas_object_image: save EVAS_IMAGE_CONTENT_HINT_DYNAMIC image

evas_object_image: save EVAS_IMAGE_CONTENT_HINT_DYNAMIC image

Summary:
evas_gl_common_image_content_hint_set makes RGBA_Image NULL if content hint
is EVAS_IMAGE_CONTENT_HINT_DYNAMIC with 'sec_tbm_surface' and 'egl_tbm_ext'.

efl_file_save(_efl_canvas_image_internal_efl_file_save_save) does not work
in this case because ENFN->image_data_direct_get returns FALSE.

This patch makes ENFN->image_data_direct_get work but you need to free its
returned data after using it.

Reviewers: Hermet, jsuya

Reviewed By: Hermet

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D8516