anv: Revive struct anv_common

anv: Revive struct anv_common

The struct was deleted by:
  commit efe9d1cde3340d3a9d17e5560b609a4fb839d43d
  Author: Edward O'Callaghan <funfunctor@folklore1984.net>
  Subject: anv: Clean up some unused variables

Unlike the original anv_common, the new one has a non-const pNext
pointer because we will use it for the output structs of
VK_KHR_get_physical_device_properties2.

v2:
  - Retype pNext from void* to struct anv_common*.

Reviewed-by: Jason Ekstranad <jason@jlekstrand.net>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>