software/bios: Add option to obtain IP address from DHCP server

[Meet909]

That PR allows to obtain IP address automatically from DHCP server using eth_dhcp command.
That command is only available when with_dhcp argument is set in litex/soc/integration/soc.py.
dhcp_get_ip function in litex/soc/software/bios/boot.c invokes dhcp_resolve function with MAC address as parameter.
That PR is associated with litex-hub/litex-boards#206.

[jluebbe]

Is there a way to generate a reproducible MAC address based on some information in the FPGA or SPI-NOR? For example a serial number?

[mithro]

@jluebbe -- Depends on the FPGA and board, some FPGAs have a "device DNA" that could potentially be used to randomly generate a MAC address. Some FPGA boards have an EEPROM with a MAC address encoded in them (like the Numato Opsis), others have an EEPROM embedded in the Ethernet PHY.

[enjoy-digital]

Thanks @MateuszKosmala, this is a very interesting feature. I'll try to review it very soon.