Now that we require locking to evict, multiple vmas from the same object
might not be evicted. This is expected and required, because execbuf will
move to short-term pinning by using the lock only. This will cause these
tests to fail, because they create a ton of vma's for the same object.

Unbind manually to prevent spurious -ENOSPC in those mock tests.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211216142749.1966107-8-maarten.lankhorst@linux.intel.com