drm/i915: Include ioctl in set-tiling and get-tiling function names

Make it clear that these functions are the user entry points for
the tiling/fence registers.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170110121045.27144-1-chris@chris-wilson.co.uk