kernel: bump to 3.10.27

kernel: Add support for HiFiBerry Digi
See: https://github.com/raspberrypi/linux/pull/501

firmware: dispmanx: fix for negative dest_rect coordines used in an element modify call
See: http://www.raspberrypi.org/phpBB3/viewtopic.php?f=67&t=66004

firmware: Add mmal headers
See: https://github.com/raspberrypi/userland/pull/138

userland: Make constant QP mode actually have constant QP
See: https://github.com/raspberrypi/userland/pull/139