SVG is not a bitmap format, and allegro doesn't support it out-of-the box.
If you want to use SVG, you'll need to use an SVG rendering library (you could write your own, but SVG is pretty complex, so it's probably way over your head), and write some glue to make it render to allegro surfaces.
An easier route is to just open the SVG in the editor of your choice (e.g. Inkscape) and export it to a bitmap format that allegro understands. If you're using A5, I'd recommend PNG - it offers lossless compression, and it supports full truecolor with alpha transparency.