pan/bi: Use nodearrays for linear constraints

pan/bi: Use nodearrays for linear constraints

Speeds up compiling shaders/skia/781.shader_test in shader-db by 8x
(Icecream95).

...At least it did before I extended to support register allocation of vec8.  On
Valhall, texture instructions require up to 8 consecutive registers. To handle
this, provide for vec8 register allocation. Liveness was already (accidentally?)
vec8. The increased memory requirement is acceptable given that the interference
matrix is now stored sparsely (Alyssa).

Icecream95 reports the vec8 changes hurt RA performance by about 1% on average.
I consider this acceptable for now.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16780>