intel/nir: Enable load/store vectorization

intel/nir: Enable load/store vectorization

This commit enables the I/O vectorization pass that was originally
written for ACO for Intel drivers.  We enable it for UBOs, SSBOs, global
memory, and SLM.  We only enable vectorization for the scalar back-end
because it vec4 makes certain alignment assumptions.

Shader-db results with iris on ICL:

    total instructions in shared programs: 16077927 -> 16068236 (-0.06%)
    instructions in affected programs: 199839 -> 190148 (-4.85%)
    helped: 324
    HURT: 0
    helped stats (abs) min: 2 max: 458 x̄: 29.91 x̃: 4
    helped stats (rel) min: 0.11% max: 38.94% x̄: 4.32% x̃: 1.64%
    95% mean confidence interval for instructions value: -37.02 -22.80
    95% mean confidence interval for instructions %-change: -5.07% -3.58%
    Instructions are helped.

    total cycles in shared programs: 336806135 -> 336151501 (-0.19%)
    cycles in affected programs: 16009735 -> 15355101 (-4.09%)
    helped: 458
    HURT: 154
    helped stats (abs) min: 1 max: 77812 x̄: 1542.50 x̃: 75
    helped stats (rel) min: <.01% max: 34.46% x̄: 5.16% x̃: 2.01%
    HURT stats (abs)   min: 1 max: 22800 x̄: 336.55 x̃: 20
    HURT stats (rel)   min: <.01% max: 17.11% x̄: 2.12% x̃: 1.00%
    95% mean confidence interval for cycles value: -1596.83 -542.49
    95% mean confidence interval for cycles %-change: -3.83% -2.82%
    Cycles are helped.

    total sends in shared programs: 814177 -> 809049 (-0.63%)
    sends in affected programs: 15422 -> 10294 (-33.25%)
    helped: 324
    HURT: 0
    helped stats (abs) min: 1 max: 256 x̄: 15.83 x̃: 2
    helped stats (rel) min: 1.33% max: 67.90% x̄: 21.21% x̃: 15.38%
    95% mean confidence interval for sends value: -19.67 -11.98
    95% mean confidence interval for sends %-change: -23.03% -19.39%
    Sends are helped.

    LOST:   7
    GAINED: 2

Most of the helped shaders were in the following titles:

 - Doom
 - Deus Ex: Mankind Divided
 - Aztec Ruins
 - Shadow of Mordor
 - DiRT Showdown
 - Tomb Raider (Rise, I think)

Five of the lost programs are SIMD16 shaders we lost from dirt showdown.
The other two are compute shaders in Aztec Ruins which switched from
SIMD8 to SIMD16.

Vulkan pipeline-db stats on ICL:

    Instructions in all programs: 296780486 -> 293493363 (-1.1%)
    Loops in all programs: 149669 -> 149669 (+0.0%)
    Cycles in all programs: 90999206722 -> 88513844563 (-2.7%)
    Spills in all programs: 1710217 -> 1730691 (+1.2%)
    Fills in all programs: 1931235 -> 1958138 (+1.4%)

By far the most help was in the Tomb Raider games.  A couple of Batman
games with DXVK were also helped.  In Shadow of the Tomb Raider:

    Instructions in all programs: 41614336 -> 39408023 (-5.3%)
    Loops in all programs: 32200 -> 32200 (+0.0%)
    Cycles in all programs: 1875498485 -> 1667034831 (-11.1%)
    Spills in all programs: 196307 -> 214945 (+9.5%)
    Fills in all programs: 282736 -> 307113 (+8.6%)

Benchmarks of real games I've done on this patch:

 - Rise of the Tomb Raider: +3%
 - Shadow of the Tomb Raider: +10%

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4367>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4367>