radeonsi: skip generic out/in indices without a shader IO index

radeonsi: skip generic out/in indices without a shader IO index

OpenGL uses at most 32 generic outputs/inputs in any stage, and they always
have a shader IO index and therefore fit into the outputs_written/
inputs_read/kill_outputs fields.

However, Nine uses semantic indices more liberally. We support that
in VS-PS pipelines, except that the optimization of killing outputs
must be skipped.

Tested-by: Dieter Nützel <Dieter@nuetzel-hh.de>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>