Use Adb over USB by default in Apalis iMX6

Adb over USB work correctly in Toradex Apalis iMX6 as long as the jumper (JP2)
is correctly set on the Ixora carrier board.

Task-number: QTEE-671
Change-Id: If1e070e532b5a8fe0eff29b125e0a690b4218c8f
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@digia.com>