lima/ppir: convert to nir_legacy

lima/ppir: convert to nir_legacy

With the upcoming transition away from nir_register and modifiers in
nir, ppir needs to prepare for those features to be removed.
The most straightforward way for ppir without major reworks at this time
is to use the new nir_legacy helpers so that most of the backend can be
kept untouched (particularly due to use of abs/neg/sat modifiers).
Do this for now to unblock the transition with little impact; ppir can
be optimized at a later moment to have its own passes which will allow
it to drop the nir_legacy use and use just the chasing helpers.

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24246>