buildroot

configs/freescale_mpc8315erdb: lock down binutils version

The used U-Boot version (2014.04) isn't too happy with newer (>= 2.25)
binutils versions, so keep it locked down until the config is updated
for a newer version.
U-Boot 2016.03 in fact does work for mpc8315erdb - however it doesn't
yet support SPL which is necessary for NAND boot and would be a massive
defconfig revamp switching to NOR.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>