samples: rework show-tuple

Now that we are using defconfig files, the samples do not contain
the full configuration, so we can not simply parse them to show
their content.

Instead, we must fake recalling a sample, and parse the generated
.config file.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

reporter_name="Remy Bohmer"

reporter_url="linux@bohmer.net"

reporter_comment="Example for building a toolchain for m68000 bare metal targets"