test/efl: Ecore_Wl_Window struct internals are private in 1.8 now

Use the new ecore_wl_window_surface_get accessor in ECORE 1.8 since
the Ecore_Wl_Window struct internals are private now.  Also maintain
backwards compatibility with ECORE 1.7 too.

Signed-off-by: U. Artie Eoff <ullysses.a.eoff@intel.com>