drm/i915: Do .init_clock_gating() earlier to avoid it clobbering watermarks

Currently ILK-BDW explicitly disable LP1+ watermarks from their
.init_clock_gating() hooks. Unfortunately that hook gets called way too
late since by that time we've already initialized all the watermark
state tracking which then gets out of sync with the hardware state.

We may eventually want to consider killing off the explicit LP1+
disable from .init_clock_gating(). In the meantime however, we can
avoid the problem by reordering the init sequence such that
intel_modeset_init_hw()->intel_init_clock_gating() gets called
prior to the hardware state takeover.

I suppose prior to the two stage watermark programming we were
magically saved by something that forced the watermarks to be
reprogrammed fully after .init_clock_gating() got called. But
now that no longer happens.

Note that the diff might look a bit odd as it kills off one
call of intel_update_cdclk(), but that's fine because
intel_modeset_init_hw() does the exact same thing. Previously
we just did it twice.

Actually even this new init sequence is pretty bogus as
.init_clock_gating() really should be called before any gem
hardware init since it can  configure various clock gating
workarounds and whatnot that affect the GT side as well. Also
intel_modeset_init() really should get split up into better
defined init stages. Another "fun" detail is that
intel_modeset_gem_init() is where RPS/RC6 gets configured.
Why that is done from the display code is beyond me. I've
decided to leave all this be for now, and just try to fix
the init sequence enough for watermarks to work.

Cc: stable@vger.kernel.org
Cc: Gabriele Mazzotta <gabriele.mzt@gmail.com>
Cc: David Purton <dcpurton@marshwiggle.net>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reported-by: Gabriele Mazzotta <gabriele.mzt@gmail.com>
Reported-by: David Purton <dcpurton@marshwiggle.net>
Tested-by: Gabriele Mazzotta <gabriele.mzt@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96645


Fixes: ed4a6a7c ("drm/i915: Add two-stage ILK-style watermark programming (v11)")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170220140443.30891-1-ville.syrjala@linux.intel.com


Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170315143158.31780-1-ville.syrjala@linux.intel.com


(cherry picked from commit 5be6e334)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>