i965: Refactor debug dumping of GLSL IR.

i965: Refactor debug dumping of GLSL IR.

This was only going to get worse when tesselation shows up, and was
causing too much extra duplication in my stderr changes coming up.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>