drm/i915: Remove delayed FBC activation.

The only time we should start FBC is when we have waited a vblank
after the atomic update. We've already forced a vblank wait by doing
wait_for_flip_done before intel_post_plane_update(), so we don't need
to wait a second time before enabling.

Removing the worker simplifies the code and removes possible race
conditions, like happening in 103167.

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103167
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180625163758.10871-2-maarten.lankhorst@linux.intel.com
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1659,11 +1659,6 @@ static int i915_fbc_status(struct seq_file *m, void *unused)
 	else
 		seq_printf(m, "FBC disabled: %s\n", fbc->no_fbc_reason);
 
-	if (fbc->work.scheduled)
-		seq_printf(m, "FBC worker scheduled on vblank %llu, now %llu\n",
-			   fbc->work.scheduled_vblank,
-			   drm_crtc_vblank_count(&fbc->crtc->base));
-
 	if (intel_fbc_is_active(dev_priv)) {
 		u32 mask;