MIPS16: Simplify extended operand handling
    
    Simplify extended operand handling and only specially process immediates
    which require bit shuffling, using the generic operand insertion and
    extraction handlers for the '<' (5-bit shift amount) operand code in
    particular.  Require the least significant bit of all extended operand
    forms to be (artificially) set to 0 for their special processing to
    trigger.
    
    	gas/
    	* config/tc-mips.c (mips16_immed): Limit `mips16_immed_extend'
    	use to operands whose LSB position is zero.
    
    	opcodes/
    	* mips-dis.c (print_mips16_insn_arg): Simplify processing of
    	extended operands.
    	* mips16-opc.c (decode_mips16_operand): Switch the extended
    	form of the `<' operand type to LSB position 22.
    
    (cherry picked from commit bdd152861ce75c36828904cf3d10f8ce14da6cf5)