efl/engines: Introduce multi_font_draw() function

efl/engines: Introduce multi_font_draw() function

This new engine function will only be used in software generic for
now - since it's the only engine used with the async render.

This function has been introduced in order to avoid growing thread
command queue too much to draw a text_props at a time on render calls
from textgrid objects.

Patch by: Paulo Alcantara <pcacjr@profusion.mobi>

SVN revision: 82832