anv: Use a separate pool for binding tables when soft pinning

anv: Use a separate pool for binding tables when soft pinning

Soft pinning lets us satisfy the binding table address
requirements without using both sides of a growing state_pool.

If you do use both sides of a state pool, then you need to read
the state pool's center_bo_offset (with the device mutex held) to
know the final offset of relocations that target the state pool
bo.

By having a separate pool for binding tables that only grows in
the forward direction, the center_bo_offset is always 0 and
relocations don't need an update pass to adjust relocations with
the mutex held.

v2: - don't introduce a separate state flag for separate binding tables (Jason)
    - replace bo and map accessors with a single binding_table_pool accessor (Jason)
v3: - assert bt_block->offset >= 0 for the separate binding table (Jason)

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>