usb: gadget: Setup DMA ops for OTG's gadget devices

A device that is not probed via DT nodes needs to setup its DMA
operations with an explicit call to arch_setup_dma_ops. The child
and grandchild gadget devices of msm_otg are not populated via DT
nodes. This patch adds the above method for these devices.

Change-Id: Ida9d63dce2cbb8c61c65cb95e0ea5f10860e8edc
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>