devtool: modify support debug-builds

devtool: modify support debug-builds

Add a new option --debug-builds to automatically add DEBUG_BUILD = “1”
to the bbappend file of this recipe. This is especially useful when
invoking devtool modify before invoking devtool ide-sdk to perform a
remote debugging session.

Signed-off-by: Adrian Freihofer <adrian.freihofer@siemens.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Steve Sakoman <steve@sakoman.com>