drm/i915/bxt: Avoid early timeout during PLL enable

Since wait_for_atomic doesn't re-check the wait-for condition after
expiry of the timeout it can fail when called from non-atomic context
even if the condition is set correctly before the expiry. Fix this by
using the non-atomic wait_for instead.

I noticed this via the PLL locking timing out incorrectly, with this fix
I couldn't reproduce the problem.

Fixes: 0351b939 ("drm/i915: Do not lie about atomic timeout granularity")
CC: Chris Wilson <chris@chris-wilson.co.uk>
CC: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
CC: drm-intel-fixes@lists.freedesktop.org
Link: http://patchwork.freedesktop.org/patch/msgid/1467110253-16046-2-git-send-email-imre.deak@intel.com
(cherry picked from commit 0b786e41)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_dpll_mgr.c

@@ -1377,8 +1377,8 @@ static void bxt_ddi_pll_enable(struct drm_i915_private *dev_priv,
 	I915_WRITE(BXT_PORT_PLL_ENABLE(port), temp);
 	POSTING_READ(BXT_PORT_PLL_ENABLE(port));
 
-	if (wait_for_atomic_us((I915_READ(BXT_PORT_PLL_ENABLE(port)) &
-			PORT_PLL_LOCK), 200))
+	if (wait_for_us((I915_READ(BXT_PORT_PLL_ENABLE(port)) & PORT_PLL_LOCK),
+			200))
 		DRM_ERROR("PLL %d not locked\n", port);
 
 	/*