Add Intel NIOS V BSP support to the RISC-V architecture

Summary

The Intel NIOS V is synthesizable verilog model of a processor that implements the RISC-V architecture in Intel FPGA products. The verilog model comes in three variants: NIOS V/c, NIOS V/m, and NIOS V/g. This BSP supports variants V/m and V/g. The V/g variant is supported with or without an FPU. The V/c variant is not supported due to it's lack of an interrupt controller.