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/1467297225-21379-54-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_sideband.c

@@ -51,7 +51,9 @@ static int vlv_sideband_rw(struct drm_i915_private *dev_priv, u32 devfn,
 
 	WARN_ON(!mutex_is_locked(&dev_priv->sb_lock));
 
-	if (wait_for((I915_READ(VLV_IOSF_DOORBELL_REQ) & IOSF_SB_BUSY) == 0, 5)) {
+	if (intel_wait_for_register(dev_priv,
+				    VLV_IOSF_DOORBELL_REQ, IOSF_SB_BUSY, 0,
+				    5)) {
 		DRM_DEBUG_DRIVER("IOSF sideband idle wait (%s) timed out\n",
 				 is_read ? "read" : "write");
 		return -EAGAIN;