Revert "board: don't hardcode interface for ti_beaglebone"

This reverts commit 7d7a43fd.

The change concerns the "Black" variant of the TI BeagleBone, while the
configuration file is for the original BeagleBone board, which actually
embeds a debug interface on the PCB.

Change-Id: I2232af210deb698f8b3c0a547f26cd0a0a8f89d0
Signed-off-by: Matthias Welwarsky <matthias@welwarsky.de>
Reviewed-on: http://openocd.zylin.com/3094


Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>