anv/allocator: Add helper to push states back to the state table.

anv/allocator: Add helper to push states back to the state table.

The use of anv_state_table_add() combined with anv_state_table_push(),
specially when adding a bunch of states to the table, is very verbose.
So we add this helper that makes things easier to digest.

We also already add the anv_state_table member in this commit, so things
can compile properly, even though it's not used.

v2: assert that the states are always aligned to their size (Jason)
v3: Add "table" member to anv_state_pool in this commit.

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