anv: destroy descriptor sets when pool gets reset

As stated in Vulkan spec:
   "Resetting a descriptor pool recycles all of the resources from all
    of the descriptor sets allocated from the descriptor pool back to
    the descriptor pool, and the descriptor sets are implicitly freed."

This fixes dEQP-VK.api.descriptor_pool.*

Fixes: 14f6275c "anv/descriptor_set: add reference counting for..."
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Tested-by: Clayton Craft <clayton.a.craft@intel.com>
(cherry picked from commit 775aabdd)

Squashed with:

anv: Fix destroying descriptor sets when pool gets reset

pool->next and pool->free_list were reset before their usage in
anv_descriptor_pool_free_set

Fixes: 775aabdd "anv: destroy descriptor sets when pool gets reset"
Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
(cherry picked from commit 9c80be95)