drm/i915: Create dumb buffer from LMEM

When LMEM is supported, dumb buffer preferred to be created from LMEM.

v2:
  Parameters are reshuffled. [Chris]
v3:
  s/region_id/mem_type
v4:
  use the i915_gem_object_create_region [chris]

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200104191043.2207314-2-chris@chris-wilson.co.uk