anv: Handle state pool relocations using "wrapper" BOs

anv: Handle state pool relocations using "wrapper" BOs

Instead of depending on a mutable BO in the state pool for handling
growing state pools, add a concept of "wrapper" BOs which just wrap an
actual BO.  This way, the wrapper can exist once for all of time and we
can put it in relocation lists even if the actual BO it references gets
swapped out.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>