drm/i915/selftests: Prepare gtt tests for obj->mm.lock removal

We need to lock the global gtt dma_resv, use i915_vm_lock_objects
to handle this correctly. Add ww handling for this where required.

Add the object lock around unpin/put pages, and use the unlocked
versions of pin_pages and pin_map where required.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210323155059.628690-61-maarten.lankhorst@linux.intel.com