kernel: Bump to 3.12.24

kernel: conifg: Add CONFIG_DEVPTS_MULTIPLE_INSTANCES
See: https://github.com/raspberrypi/linux/pull/603

firmware: dispmanx: Fix snapshot scaling when a fullscreen dest rect is used
See: https://github.com/raspberrypi/firmware/issues/295

firmware: dispmanx: allow rotations into 24-bit memory displays
See: https://github.com/raspberrypi/firmware/issues/267

firmware: Add MMAL parameter for render stats
See: https://github.com/raspberrypi/firmware/issues/287

firmware: image_decode: Move decode thread to second core
This improves jpeg decode time a little

firmware: imagefx: Separate out the fast 1080i deinterlace algorithm
As the 1080i deinterlace doesn't require the 3 frames of context we can save ~6MB by requesting it explicitly