kernel: Bump to 3.12.31

kernel: vchiq: Take care of a corner case tickled by VCSM, and enable in kernel
See: https://github.com/raspberrypi/linux/commit/7afe2b7073258c4641a6f32868a58a7715d2a136

kernel: enable USBTV module and add patch for PAL support
See: https://github.com/raspberrypi/linux/issues/711