drm/i915/skl: Consider plane rotation when calculating stride in skl_do_mmio_flip

Previously rotation was ignored and wrong stride programmed
into the plane registers resulting in a corrupt image on screen.

v2: Do not access potentialy old plane state at flip time,
    but store the rotation value at the time of queing the flip.
    (Ville)

v3: No need to pass rotation to intel_queue_mmio_flip since it
    is available in the crtc. (Ville)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Testcase: igt/kms_rotation_crc/primary-rotation-90-flip-stress (SKL)
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Sonika Jindal <sonika.jindal@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>