* mips.h: Assign 'm'/'M' codes to MIPS16e save/restore

    * mips.h: Assign 'm'/'M' codes to MIPS16e save/restore
        instructions.  Define MIPS16_ALL_ARGS and MIPS16_ALL_STATICS for
        save/restore encoding of the args field.

        * mips16-opc.c: Add MIPS16e save/restore opcodes.
        * mips-dis.c (print_mips16_insn_arg): Handle printing of 'm'/'M'
        codes for save/restore.

        * config/tc-mips.c (mips16_ip): Add handling of 'm' and 'M' codes
        for the MIPS16e save/restore instructions.

        * gas/mips/mips.exp: Run new save/restore tests.
        * gas/testsuite/gas/mips/mips16e-save.s: New test for generating
        different styles of save/restore instructions.
        * gas/testsuite/gas/mips/mips16e-save.d: New.