drm/i915: Report the actual swizzling back to userspace

Userspace cares about whether or not swizzling depends on the page
address for its direct access into bound objects. Extend the get_tiling
ioctl to report the physical swizzling value in addition to the logical
swizzling value so that userspace can accurately determine when it is
possible for manual detiling.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Akash Goel <akash.goel@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Testcase: igt/gem_tiled_wc
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>