radeonsi: precompute more spi_map code

radeonsi: precompute more spi_map code

This replaces vs_output_param_offset by vs_output_ps_input_cntl,
which is easier to use.

For geometry shaders, vs_output_ps_input_cntl is stored in the GS si_shader
structure, not gs_copy_shader. This requires that gs_copy_shader compilation
is finished before the GS main shader part, so that GS can initialize
vs_output_ps_input_cntl using the compiled GS copy shader.

output_semantic_to_slot becomes unused, so it's removed.

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12343>