A lot of the code in set_base is uncessary when the crtc is off, so we
can get rid of it all. Also, we don't need to call the fbc/psr update
functions since the crtc enable/disable hooks do that already.

The only things we really need are:
- Pin the new framebuffer and potentially unpin the old framebuffer
  (if the crtc has been on and we only change the configuration).
- Update the plane registers.

The first step will move out of platform code with the very next
patch.

v2: Don't forget about haswell ...
Reviewed-by: Akash Goel <akash.goel@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>