FreeBSD on Altera Cyclon 5 (DE1-SoC-MTL)

Nios II is a soft-core Wishbone-compatible RISC processor.
Not sure that FreeBSD has a corresponding port.
Since it's a soft-core, in theory one can use lowRISC (RISC-V for SoC, FPGAs etc.) instead.
The current status of RISC-V port is here:
However it's a very new project and does not support lowRISC yet.