nir/lower_doubles: Inline functions directly in lower_doubles

nir/lower_doubles: Inline functions directly in lower_doubles

Instead of trusting the caller to already have created a softfp64
function shader and added all its functions to our shader, we simply
take the softfp64 shader as an argument and do the function inlining
ouselves.  This means that there's no more nasty functions lying around
that the caller needs to worry about cleaning up.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>