drm/i915/selftests: add igt_vma_move_to_active_unlocked

All calls to i915_vma_move_to_active are surrounded by vma lock
and/or there are multiple local helpers for it in particular tests.
Let's replace it by common helper.
The patch should not introduce functional changes.

Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221019215906.295296-3-andrzej.hajda@intel.com