intel/compiler: Update block IPs once in register_coalesce

intel/compiler: Update block IPs once in register_coalesce

Performance improvement in
dEQP-VK.ssbo.phys.layout.random.16bit.scalar.13 for n=30:

release build (w/Fedora build flags): -0.82% ± 0.23%
Meson -Dbuildtype=debugoptimized:     -0.74% ± 0.27%

The difference in the debugoptimized build is the calls to
inst_is_in_block(block, this) still exist on each call to remove().

v2: Only update each block's IP data once instead of once per block.
Suggested by Emma.

Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11632>