nouveau: Use nir_lower_doubles instead of lower_fmod64 on nvc0.

nouveau: Use nir_lower_doubles instead of lower_fmod64 on nvc0.

We currently have two duplicate mechanisms for lowering fmod@64.
One is a nir_opt_algebraic rule keyed off of options->lower_fmod64,
and the other is nir_lower_doubles, which offers a full gamut of
fp64 lowering.  The latter works slightly better in some corner cases,
so I'm trying to eliminate lower_fmod64 and drop the redundancy.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>