intel/fs/ra: Sanity-check our IP counts

intel/fs/ra: Sanity-check our IP counts

Starting with e99081e76d4a, we don't re-construct liveness information
every time we spill a register.  Instead, we're very careful to track
which instructions are spill instructions and not contribute those to
the IP count so that we can continue to use the old liveness information
even though instructions have been added.  This commit adds an assert
that sanity-checks that we count the same number of instructions as our
liveness information is based on.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7084>