anv: Re-arrange push constant data a bit

anv: Re-arrange push constant data a bit

This moves the compute stuff into a anv_push_constants::cs sub-struct.
It also moves dynamic offsets into the push constants.  This means we
have to duplicate the data per-stage but that doesn't seem like the end
of the world and one day we may wish to make dynamic offsets per-stage
anyway.

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