buildroot

configs: add pylibfdt where necessary

Add TARGET_UBOOT_NEEDS_PYLIBFDT to all defconfigs, where u-boot needs
Python libfdt to build.

Signed-off-by: Vincent Stehlé <vincent.stehle@laposte.net>
Cc: Jagan Teki <jagan@amarulasolutions.com>
Cc: Mike Harmony <mike.harmony@snapav.com>
Cc: Sergey Matyukevich <geomatsi@gmail.com>
Cc: Jan Kraval <jan.kraval@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>