drm/i915: Rename the rotated gtt view member to 'rotated'

Also rename 'rotation_info' to 'rotated' to match the view type exactly,
this should avoid confusion which union members is valid for each view
type.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1453316739-13296-2-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>