BIt manipulation register file operand usage

Created by: Silabs-ArjanB

The current B decoder causes a register file read for both operands for all bit manipulation instructions:

decoder_ctrl_o.rf_re[0]         = 1'b1;
decoder_ctrl_o.rf_re[1]         = 1'b1;

This is not correct; for example CLZ only uses RS1 as source. All instructions should be checked and corrected if needed.