usb: dwc3: turn off VBUS when leaving host mode

VBUS should be turned off when leaving the host mode.
Set GCTL_PRTCAP to device mode in teardown to de-assert DRVVBUS pin to
turn off VBUS power.

Fixes: 5f94adfe ("usb: dwc3: core: refactor mode initialization to its own function")
Cc: stable@vger.kernel.org
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>