Add Linux UART16550 validation tests

[arturum1]

Please create tag M3_b after merging this PR.

Updated Py2HWSW to latest version: IObundle/py2hwsw#433

To try it out, run the following commands:

# Generate and run the SoCLinux system in the aes_ku040_db_g FPGA board:
make fpga-build fpga-run BOARD=iob_aes_ku040_db_g

# Run the Linux OS on the FPGA board:
# The system will automatically launch the UART validation tests upon boot.
make fpga-run BOARD=iob_aes_ku040_db_g RUN_LINUX=1 UART_DEMO=1