drm/bochs: atomic: use suspend/resume helpers

Switch to atomic helpers: drm_mode_config_helper_suspend/resume().

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20190111053752.4004-9-kraxel@redhat.com