i965: Use the same nir options for all gens
i965: Use the same nir options for all gens

If we tell NIR to split ffma's, then we don't need seperate options
anymore.

Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler