usb: dwc3: Add USB_DR_MODE_DRD as dual role mode

dwc_usb31 supports DRD only mode. It does not support
USB OTG mode. SNPS core consultant parameter DWC_USB3_EN_OTG
is not set for dwc_usb31. Hence add USB_DR_MODE_DRD which
reflects support for host and device mode support without
supporting USB OTG features.

Change-Id: I63841b9fb47ff9db09b8a1ac5cbb5bff069c2ef4
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>