fb_bits is useful to have in the crtc_state for cs flips when
the code is updated to use intel_frontbuffer_flip_prepare/complete.
So calculate it in advance and move it to crtc_state. The other stuff
can be calculated in post_plane_update, and aren't useful elsewhere.

Changes since v1:
- Changing wording, remove comment about loop.
Changes since v2:
- Rebase.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1457516145-32117-1-git-send-email-maarten.lankhorst@linux.intel.com