drm/i915: FB backing gem obj should reside in LMEM

If Local memory is supported by hardware, we want framebuffer backing
gem objects from local memory.

if the backing obj is not from LMEM, pin_to_display is failed.

v2:
  memory regions are correctly assigned to obj->memory_regions [tvrtko]
  migration failure is reported as debug log [Tvrtko]
v3:
  Migration is dropped. only error is reported [Daniel]
  mem region check is move to pin_to_display [Chris]
v4:
  s/dev_priv/i915 [chris]
v5:
  i915_gem_object_is_lmem is used for detecting the obj mem type. [Matt]

cc: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Ramalingam C <ramalingam.c@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/20191105144414.30470-1-ramalingam.c@intel.com