anv: Reduce the minimum number of relocations

anv: Reduce the minimum number of relocations

The original value of 256 was under the assumption that you're a batch
buffer which is likely going to have a large number of relocations.
However, pipeline objects on Gen7 will have at most 6 relocations (one
per shader stage and one for the workaround BO) so this is a lot of
per-pipeline wasted space.

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