Illegal Funct3 Value for IW instructions is not marked as such

Created by: AlecVercruysse

When executing the instruction 0x0000701B (an integer-word instruction): op = 0b0011011, funct7 = 0b0000000, with an illegal funct3: funct3 = 0b111, the case statement in line 175 of controller.sv fires, marking it as a valid instruction. There is no valid IW instruction with funct3=b111.

IFunctD in ieu/controller.sv should de-assert in this case, so the instruction is marked as invalid.