drm/i915/display: Suspend MST topology manager before destroy fbdev

MST topology needs to be suspended so we don't have any calls to
fbdev after it's finalized. MST will be destroyed later as part of
drm_mode_config_cleanup().

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109964


Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191127021609.162700-1-jose.souza@intel.com