[Mesa-dev] some initial fp64 lowering to fix some cayman tests

[Dave Airlie]

Elie has been working on soft-fp64 code in a branch for a while,
and I've been slowly helping trying to get it in place so we can
enable GL4.x on the evergreen GPUs.

However I've discovered on cayman we don't have int->double or
uint->double support, and my conversion functions which did
(int->f32->f64, and uint->f32->f64) weren't passing CTS tests
or piglits.

Instead of trying to do all this work in the r600 shader code,
I've decided to start bringing in some of Elie's work now, and using
it to fix the problem.

This isn't soft-fp64, but it adds some of the required infrastructure
that it will need, and might be an easier way to start introducing
the big picture.

Dave.