buildroot

utils/diffconfig: add diffconfig utility

Diffconfig is a simple utility for comparing two configuration files.
See usage in the script for more info.

Borrowed from the Linux kernel source code and adapted to Buildroot.

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>