samples: use savedefconfig when saving samples

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>

# m68k specific configuration file

## depends on EXPERIMENTAL

##

## select ARCH_SUPPORTS_32

## select ARCH_DEFAULT_32

## select ARCH_DEFAULT_BE

## select ARCH_SUPPORTS_WITH_CPU

##

## help The m68k architecture