configs/beaglebone: add DT for the Beaglebone Black Wireless

The Beaglebone Black Wireless needs a specific DT, which u-boot tries to
load based on the board name. Make sure we ship the DT so that we can
boot on that platform.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>