Wrong Illegal instruction fault for compressed fld ft0, xxx(sp)

Created by: xushengj

If a compressed instruction fld rd, xxx(sp) use ft0 as rd, currently Ariane will generate an illegal instruction fault, caused by the check at src/compressed_decoder.sv:205: if (instr_i[11:7] == 5'b0) illegal_instr_o = 1'b1; However, the restriction that destination shouldn't be zero should only be applied to GPR.

Suggest to remove src/compressed_decoder.sv:205 to fix the fault.