drm/xe: Ensure that we don't access the placements array out-of-bounds

Ensure, using xe_assert that the various try_add_<placement> functions
don't access the bo placements array out-of-bounds.

v2:
- Remove the places argument to make sure the xe_assert operates on
  the array we're actually populating. (Matthew Auld)

Suggested-by: Ohad Sharabi <osharabi@habana.ai>
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/946


Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Ohad Sharabi <osharabi@habana.ai> #v1
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231123153158.12779-2-thomas.hellstrom@linux.intel.com


Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>