drm/i915/fbc: make FBC work with fastboot

Move intel_fbc_enable to a place where it is called regardless of the
"modeset" variable, and make sure intel_fbc_enable can be called
multiple times without intel_fbc_disable being called.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1453210558-7875-20-git-send-email-paulo.r.zanoni@intel.com
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 69ab077..a832ff1 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13558,7 +13558,6 @@
 		if (modeset && crtc->state->active) {
 			update_scanline_offset(to_intel_crtc(crtc));
 			dev_priv->display.crtc_enable(crtc);
-			intel_fbc_enable(intel_crtc);
 		}
 
 		if (update_pipe) {
@@ -13571,6 +13570,9 @@
 		if (!modeset)
 			intel_pre_plane_update(intel_crtc);
 
+		if (crtc->state->active && intel_crtc->atomic.update_fbc)
+			intel_fbc_enable(intel_crtc);
+
 		if (crtc->state->active &&
 		    (crtc->state->planes_changed || update_pipe))
 			drm_atomic_helper_commit_planes_on_crtc(crtc_state);