usb: dwc2: Update DMA descriptor structure

Rename DMA descriptor structure from dwc2_hcd_dma_desc to dwc2_dma_desc
as it is applies to both host and gadget.

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>