usb: phy: msm: Handle disconnect events

Put the transceiver in non-driving mode. Otherwise host
may not detect soft-disconnection.

Signed-off-by: Ivan T. Ivanov <iivanov@mm-sol.com>
Cc: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>