tools: moveconfig: report when defconfig is updated

There are various factors that determine if the given defconfig is
updated, and it is probably what users are more interested in.

Show the log when the defconfig is updated.  Also, copy the file
only when the file content was really updated to avoid changing
the time stamp needlessly.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>