freedreno/ir3: rework setup_{input,output} to make struct varyings work

freedreno/ir3: rework setup_{input,output} to make struct varyings work

Rework setup_{input,output} to be called during emit_intrinsic, in a way
which allows struct/array/matrix type varyings to work.

This allows turnip to pass dEQP-VK.glsl.linkage.varying.struct.*

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6181>