FPU fails when supervisor mode is not supported

Created by: jordancarlin

When S_SUPPORTED is set to 0 and F_SUPPORTED is set to 1, the archXXf tests fail and get stuck in a loop of illegal instructions (as seen below)

Program fetched illegal instruction 0x00000000 from address 0x00000000. Might be fault with no fault handler.

Floating point should not be dependent on privilege modes being supported, just Zicsr. None of the current derived configurations test with s/u modes disabled (other than the ones based on simpler configs like rv32imc), which is likely why this has not been discovered.