usb: ehci: EHSET Test-Fixture device driver for host compliance

An EHSET test fixture is used to initiate test modes on an embedded
host controller while performing the usb host compliance testing.

During enumeration by the USB host this test fixture presents a VID/PID
pair and this PID value corresponds to the requested testmode.

Change-Id: I7558f9c1c37b3c65be2b358d964b295593c021d9
CRs-Fixed: 174266
Signed-off-by: Manu Gautam <mgautam@qualcomm.com>