kernel: Bump to 3.12.19

kernel: config: enable CONFIG_VIDEO_STK1160_COMMON
See: https://github.com/Hexxeh/rpi-firmware/issues/47

firmware: vdec3: h264: Improve results on some corrupt streams.
See: https://github.com/raspberrypi/firmware/issues/255

firmware: Update to HW cursor handling. Now supports overscan and arbitrary framebuffer sizes in GPU so X driver does not need to worry about it
See: http://www.raspberrypi.org/forums/viewtopic.php?f=38&t=69926

userland: RaspiVid: Fix file splitting code.
See: https://github.com/raspberrypi/userland/pull/168