OpenPiton Polara FPGA with plic

Created by: elisabethumblet

This PR adds support for FPGA emulation of Polara. More specifically it adds the following:

• Adding ALVEO U280 board as a target for FPGA implementation of Polara.

• Adds timing and implementation constraint for Vivado synthesis.

• Logic to instantiate top-level FPGA module for Openpiton framework.

• Scripts for automating synthesis and implementation using Vivado in Openpiton framework.