anv/allocator: Use anv_state_table on anv_state_pool_alloc.

anv/allocator: Use anv_state_table on anv_state_pool_alloc.

Use anv_state_pool_return_blocks() to return blocks to the pool, instead
of manually pushing them.

v3:
 - return blocks from the end of the chunk (Jason).

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