drm/i915: Fix init_clock_gating for resume

Moving the init_clock_gating() call from intel_modeset_init_hw() to
intel_modeset_gem_init() had an unintended effect of not applying
some workarounds on resume. This, for example, cause some kind of
corruption to appear at the top of my IVB Thinkpad X1 Carbon LVDS
screen after hibernation. Fix the problem by explicitly calling
init_clock_gating() from the resume path.

I really hope this doesn't break something else again. At least
the problems reported at https://bugs.freedesktop.org/show_bug.cgi?id=103549
didn't make a comeback, even after a hibernate cycle.

v2: Reorder the init_clock_gating vs. modeset_init_hw to match
    the display reset path (Rodrigo)

Cc: stable@vger.kernel.org
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Fixes: 6ac43272 ("drm/i915: Move init_clock_gating() back to where it was")
Reviewed-by: NRodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171116160215.25715-1-ville.syrjala@linux.intel.comSigned-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>

drivers/gpu/drm/i915/i915_drv.c

@@ -1714,6 +1714,7 @@ static int i915_drm_resume(struct drm_device *dev)
 	i915_gem_resume(dev_priv);
 
 	intel_modeset_init_hw(dev);
+	intel_init_clock_gating(dev_priv);
 
 	spin_lock_irq(&dev_priv->irq_lock);
 	if (dev_priv->display.hpd_irq_setup)