anv: Use a bitset for tracking residency

anv: Use a bitset for tracking residency

Now that we can conveniently map between GEM handles and struct anv_bo
pointers, we can use a simple bitset for residency tracking instead of
the complex hash set.  This shaves about 3% off of a CPU-limited example
running with the Dawn WebGPU implementation.

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