Revert "drm/i915: Add two-stage ILK-style watermark programming (v10)"

This reverts commit 396e33ae

.

This commit was triggering some FIFO underrun warnings on ILK-IVB
platforms (but surprisingly not on HSW/BDW that share more or less the
same codepaths).  These underruns were caught by the continuous
integration (CI) system and could be reproduced consistently when
running the basic acceptance tests (BAT) on the affected platforms.

Note that this revert will cause a visible regression for some
end-users; the "flicker when mouse moves between monitors in X" issue
that was reported before this patch was merged will now return.  However
regressions that are visible to CI have higher priority since they
prevent proper testing of future patches on those platforms.  Hopefully
we'll be able to figure out the cause of the underruns quickly and
remerge an improved version of this patch to fix the regression.

Cc: Daniel Vetter <daniel@ffwll.ch>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93640
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1453232584-8543-1-git-send-email-matthew.d.roper@intel.com
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>