Add lwIP TCP/IP stack using FreeRTOS tasks

[npetersen2]

• Replicate existing functionality in codebase, but port to FreeRTOS
• Initial goal: CLI over Ethernet (just like current codebase)

[codecubepi]

Xilinx provides echo server that makes lwIP work in the context of FreeRTOS.

The AMDC has existing code to handle Ethernet. See the while() loop in app_cpu0 main.c

I will need to find a way to merge these two implemenations, or at least verify that the Xilinx-provided implementation matches our current functionality.

[codecubepi]

Investigate other FreeRTOS 'heap_X.c' implementations to see if they can be used to revamp the logging interface, per the discussion in the Dec 12 Firmware Meeting.