cml1: correct diffconfig output format

cml1: correct diffconfig output format

If used with some packages using kconfig mechanism, the diffconfig
command generates wrong output format. Diff provides all options to
format the output correctly. This method formats as intended, is more
robust and works with the merge_config.h script from yocto-kernel-tools.

(From OE-Core rev: 1d9d035f07be1cef2764949d84cecbff7dd428dd)

Signed-off-by: Stefan Müller-Klieser <s.mueller-klieser@phytec.de>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>