usb: dwc2: gadget: Transfer length limit checking for DDMA

Add dwc2_gadget_get_chain_limit() function and its call in transfer
start routine to correctly estimate one go on transfer size if
descriptor DMA mode is selected.

Signed-off-by: Vahram Aharonyan <vahrama@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>