usb: musb: ux500: add ux500 specific code for gadget side

Although U8500 and U5500 platforms use paltform dma, Inventra dma specific code
can work for them for the most part. Only difference is for the Rx path where
this patch is making use of request->short_not_ok to select dma mode.

Signed-off-by: Mian Yousaf Kaukab <mian.yousaf.kaukab@stericsson.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>