qxl: allow creation of pre-pinned objects and use for releases.

In order to fix an issue with reservations we need to create the releases
as pre-pinned objects, this changes the placement interface and bo creation
interface to allow creating pinned objects to save nested reservations later.

This is just a stepping stone to main fix which follows to actually fix how
qxl deals with reservations.

Signed-off-by: Dave Airlie <airlied@redhat.com>