usb: dwc2: gadget: Start and complete DDMA isoc transfers

For DDMA mode in case of isochronous transfers completion performed
differently than other transfer types. This is because each usb request
was mapped to one descriptor in the chain and SW gets xfercomplete
interrupt on all descriptors. The endpoint remains enabled until HW
processes last descriptor with "L" bit set or BNA interrupt gets
asserted for IN and OUT endpoints correspondingly.

Add function dwc2_gadget_complete_isoc_request_ddma() - completes one
isochronous request taken from endpoint's queue.

Add function dwc2_gadget_start_next_isoc_ddma() - tries to restart
isochronous endpoint if requests are pending. Check for EPENA. If the
endpoint was disabled, try to restart it after programming descriptor
chain prepared by SW earlier, switch SW to fill the other half of chain.

Add function dwc2_gadget_fill_isoc_desc() - initializes DMA descriptor
for isochronous transfer based on the received request data and endpoint
characteristics.

Added function dwc2_gadget_start_isoc_ddma() - prepare DMA chain for
isochronous transfer in DDMA, programs corresponding DMA address to
DEPDMA, enables the endpoint. This function is called once SW decides to
start isochronous IN or OUT transfer depend on reception of NAK or
OUTTknEPdis interrupts indicating first isochronous token arrival from
host.
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>