ir3/postsched: Rewrite delay handling

ir3/postsched: Rewrite delay handling

Analogous to the pre-RA scheduler. Unfortunately this time it's a bit
more involved because we have to correctly handle (rptN), which is
already relevant for swz. This means we need the index of the
destination register that conflicts with the source register, to handle
swz, and we need to expose that part of ir3_delay. But once that's done,
we can delete ir3_delay_calc_postra.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13722>