The descriptor set layout code in our driver has undergone many changes
over the years.  Some of the fields which were once essential are now
useless or nearly so.  The has_dynamic_offsets field was completely
unused accept for the code to set and hash it.  The per-stage indices
were only being used to determine if a particular binding had images,
samplers, etc.  The fact that it's per-stage also doesn't matter because
that binding should never be accessed by a shader of the wrong stage.

This commit deletes a pile of cruft and replaces it all with a
descriptive bitfield which states what a particular descriptor contains.
This merely describes the data available and doesn't necessarily dictate
how it will be lowered in anv_nir_apply_pipeline_layout.

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