efl: simplify the enum to only use Cubic Bezier curve.

efl: simplify the enum to only use Cubic Bezier curve.

So SVG support all kind of primitive, but really they are just sugar
on top of the simpler cubic bezier curve. Let's simplify our backend
by just supporting them and the simple line. We still provide all
the sugar, but via helper function that do convert to the right
number of Bezier curve.