i965/fs: Allocate fragment output temporaries on demand.
i965/fs: Allocate fragment output temporaries on demand.

This gets rid of the duplication of logic between nir_setup_outputs()
and get_frag_output() by allocating fragment output temporaries lazily
whenever get_frag_output() is called.  This makes nir_setup_outputs()
a no-op for the fragment shader stage.

Reviewed-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler