anv: Delay allocation of relocation lists

anv: Delay allocation of relocation lists

The old relocation list code always allocated 256 relocations and a hash
set up-front without knowing whether or not we really need them.  In
particular, in the softpin case, this is two fairly large allocations
that we don't need to be making.  Also, for pipeline objects on haswell
where we don't have softpin, we don't need relocations unless scratch is
used so this is extra data per-pipeline.  Instead, we should do it
on-demand.  This shaves 3.5% off of a cpu-limited example running with
the Dawn WebGPU implementation.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>