i965/fs: Add support for 16-wide dispatch with uniforms in use.

i965/fs: Add support for 16-wide dispatch with uniforms in use.

This is glued in in a bit of an ugly way -- we rely on the uniforms
having been set up by 8-wide dispatch, and we just reuse them without
the ability to add new uniforms for any reason, since the 8-wide
compile is already completed.  Today, this all works out because our
optimization passes are effectively the same for both and even if they
weren't, we don't reduce the set of uniforms pushed after
optimization.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>