defconfig: sdx: Enable EHSET Test Fixture device driver

Enable required EHSET Test fixture driver to perform the high speed
electrical testing procedure for USB-IF compliance for sdx20.

Change-Id: Ie0859b15c757f278a8f4f9f6544f5969196e0fd8
Signed-off-by: Devdutt Patnaik <dpatnaik@codeaurora.org>