drm/i915: Add 180 degree sprite rotation support

The sprite planes (in fact all display planes starting from gen4)
support 180 degree rotation. Add the relevant low level bits to the
sprite code to make use of that feature.

The upper layers are not yet plugged in.

v2: HSW handles the rotated buffer offset automagically

v3: BDW also handles the rotated buffer offset automagically

Testcase: igt/kms_rotation_crc
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Sagar Kamble <sagar.a.kamble@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>