ir3: Convert to register intrinsics

ir3: Convert to register intrinsics

Thanks to our SSA-based RA, we only use nir_register for arrays, and we only
access array registers with dedicated moves anyway. So there's no reason to need
any fancy coalescing... we can just switch to register access intrinsics and
translate them to moves exactly like we would've done when getting srcs/dests
before.

This addresses the ir3 portion of #9051.

No shader-db changes with a (significant subset of) Rob's shader-db. (Some
shaders are affected by this change but not in any way that shows up in the
stats.)

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24126>