configs/stm32f469_disco_xip: explicitly set the kernel version
The version of the kernel and its headers must be explicitly set because
if you keep the default setting, the kernel is continuously updated in
buildroot with the risk that its image + dtb grow so much that it again
exceeds the 2 MByte of the flash module.
Signed-off-by: Dario Binacchi <dariobin@libero.it>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>