drm/i915: Store the final plane stride in plane_state

Let's store the final plane stride in the plane state. This avoids
having to pick between the normal vs. rotated stride during hardware
programming. And once we get GTT remapping the plane stride will
no longer match the fb stride so we'll need a place to store it
anyway.

v2: Keep checking fb->pitches[0] for cursor as later on we won't
    populate plane_state->color_plane[0].stride for invisible planes
    and we have been checking the cursor fb stride even for invisible
    planes
v3: s/betwen/between in commit msg (José)
v4: Check color_plane[0].stride instead of fb->pitches[0] in
    the skl_check_main_surface() X-tiling kludge

Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180911150139.23922-1-ville.syrjala@linux.intel.com