st/pbo: fix pbo uploads without PIPE_CAP_TGSI_VS_LAYER_VIEWPORT and skip gs

st/pbo: fix pbo uploads without PIPE_CAP_TGSI_VS_LAYER_VIEWPORT and skip gs

the previous commit handling this forced geometry shader usage for all cases,
but this is not ideal, so instead there are now fragment shader variants for
both depth==1 and depth!=1, corresponding to the existence of gl_Layer in the
shader

Fixes: 614c77772ac ("st/pbo: fix pbo uploads without PIPE_CAP_TGSI_VS_LAYER_VIEWPORT")

Acked-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8089>