qemu/arm-versatile: roll back to 3.11.x kernel series

As pointed by Thomas P. kernel 3.12 oopses when loading/using the
emulated network.
Seems 3.12 broke versatile for qemu like in the past, only in a more
subtle way this time that escaped my automated qemu builds/tests.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>