drm/i915: Convert wait_for(I915_READ(reg)) to intel_wait_for_register()

By using the out-of-line intel_wait_for_register() not only do we can
efficiency from using the hybrid wait_for() contained within, but we
avoid code bloat from the numerous inlined loops, in total (all patches):

   text    data     bss     dec     hex filename
1078551    4557     416 1083524  108884 drivers/gpu/drm/i915/i915.ko
1070775    4557     416 1075748  106a24 drivers/gpu/drm/i915/i915.ko

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1467297225-21379-36-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_dsi_pll.c

@@ -234,8 +234,11 @@ static void bxt_disable_dsi_pll(struct intel_encoder *encoder)
 	 * PLL lock should deassert within 200us.
 	 * Wait up to 1ms before timing out.
 	 */
-	if (wait_for((I915_READ(BXT_DSI_PLL_ENABLE)
-					& BXT_DSI_PLL_LOCKED) == 0, 1))
+	if (intel_wait_for_register(dev_priv,
+				    BXT_DSI_PLL_ENABLE,
+				    BXT_DSI_PLL_LOCKED,
+				    0,
+				    1))
 		DRM_ERROR("Timeout waiting for PLL lock deassertion\n");
 }