staging: vboxvideo: Fold vbox_drm_resume() into vbox_pm_resume()

vbox_pm_resume() is the only caller of vbox_drm_resume(), so squash the
2 functions into 1.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>