usb: gadget: qdss: Use the restart callback for gadget restart

Commit f937641b ("usb: dwc3: Add support for POR
upon composition switch") added a new callback 'restart' to the
usb_gadget_ops, which performs full hardware reset and
re-initialization by turning vbus off and then turning it on.
msm_dwc3_restart_usb_session() performs the same operation as
the 'restart' callback. Hence use this callback mechanism in
function drivers instead of exporting an API from dwc3-msm driver.

Change-Id: I2cef087c91895dd15dd12b46138861d7ae4e6ebb
Signed-off-by: Azhar Shaikh <azhars@codeaurora.org>