usb: gadget: tegra-xudc: Support multiple device modes

This change supports limited multiple device modes by:
- At most 4 ports contains OTG/Device capability.
- One port run as device mode at a time.

Signed-off-by: Nagarjuna Kristam <nkristam@nvidia.com>
Acked-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>