evas vg: optimize gradient sequences.

evas vg: optimize gradient sequences.

Summary:
1. Pointed out gradient prepare step triggered duplicatedly,
because they are immediate children of container.
But gradients is desigend to fill shape,
shape could get ready of the gradients which are applied to.
So, container doesn't need to prepare gradient children.

2. Ector shape does prepare its gradient renderer in it's prepare time,
each gradients objects doesn't need to prepare renderer separately.

Here code skip duplication of sequences of gradients preparation step.
by cleaning up logic.

Reviewers: #committers

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D7269

Change-Id: Ia0132b333756201ad9cf84a4b261f79e7eaa6d97