Added comms cape gateware component and usage document
This PR aims to add changes required in I/Os to allow support for the BeagleBoard comms cape.
- The component is built from the default cape gateware.
- I/Os for CAN, RS485, were reassigned for supporting the cape.
- All I/Os were tested from linux with a usage document right in the gateware folder.
Please let me know if any changes are required!