Issue illegal instruction for deconfigured B extensions

Created by: silabs-oivind

Illegal instruction won't be issued from the B decoder if trying to execute a deconfigured instruction.

In the example below (and other similar ones), add "else decoder_ctrl_o = DECODER_CTRL_ILLEGAL_INSN":

     {7'b001_0000, 3'b010}: begin // Shift left by 1 and add (sh1add)
        if (RV32B_ZBA) begin
          decoder_ctrl_o.alu_operator = ALU_B_SH1ADD;
        end
      end