anv/allocator: Add anv_state_table.

anv/allocator: Add anv_state_table.

Add a structure to hold anv_states. This table will initially be used to
recycle anv_states, instead of relying on a linked list implemented in
GPU memory. Later it could be used so that all anv_states just point to
the content of this struct, instead of making copies of anv_states
everywhere.

One has to call anv_state_table_add(), which returns an index for the
state in the table, and then get a pointer to such index, and finally
fill in the rest of the struct.

TODO:
   1) There's a lot of common code between this table backing store
   memory and the anv_block_pool buffer, due to how we grow it. I think
   it's possible to refactory this and reuse code on both places.

   2) Add unit tests.

v3:
 - Rename state table memfd (Jason)
 - Return VK_ERROR_OUT_OF_HOST_MEMORY on more places (Jason)
 - anv_state_table_grow returns VkResult (Jason)
 - Rename variables to be more informative (Jason)
 - Return errors on state table grow.
 - Rename anv_state_table_push/pop to anv_free_list_push2/pop2
   This will be renamed again to remove the trailing "2" later.

v4:
 - Remove exit(-1) from anv_state_table (Jason).
 - Use uint32_t "next" field in anv_free_entry (Jason).

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>