drm/i915: Partial revert of atomic watermark series

It's been reported that the atomic watermark series triggers some
regressions on SKL, which we haven't been able to track down yet.  Let's
temporarily revert these patches while we track down the root cause.

This commit squashes the reverts of:
  76305b1a drm/i915: Calculate watermark configuration during atomic check (v2)
  a4611e44 drm/i915: Don't set plane visible during HW readout if CRTC is off
  a28170f3 drm/i915: Calculate ILK-style watermarks during atomic check (v3)
  de4a9f83 drm/i915: Calculate pipe watermarks into CRTC state (v3)
  de165e0b

 drm/i915: Refactor ilk_update_wm (v3)

Reference: http://lists.freedesktop.org/archives/intel-gfx/2015-October/077190.html
Cc: "Zanoni, Paulo R" <paulo.r.zanoni@intel.com>
Cc: "Vetter, Daniel" <daniel.vetter@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>