drm/i915: make local-memory probing a GT operation

drm/i915: make local-memory probing a GT operation

Device local memory is very much a GT thing, therefore it should be the
responsibility of the GT to setup the device local memory region.

Suggested-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20210127131417.393872-1-matthew.auld@intel.com
[danvet: Rebase conflict.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>