When saving a sample, use savedefconfig instead of copying
the full .config file.
This reduces the saved .config, and reduces clutter when it
is later upgraded.
Also use defconfig when retrieving a sample.
Reported-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>