scripts/oe-setup-builddir: make it known where configurations come from

"with some default values" isn't clear; if the user wants to change or
inspect the default values and their history, we should help them find
where they are. This becomes especially important when using template
configs other than poky's.

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>