usbdebug: Add BeagleBone Black

Avoid some confusion as the selection of "BeagleBone" is not compatible
with the product "BeagleBone Black".

Change-Id: If73f80565cd26d2b41db972b4474ab85b609c1ad
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/4289
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>