usb: dwc3; ep0: Modify _dwc3_ep0_start_trans_ API to take 'chain' parameter

No functional change. Added a new parameter in _dwc3_ep0_start_trans_ to
indicate whether the TRB is a chained TRB or last TRB. This is in
preparation for adding chained TRB support for ep0.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>