arc: Implement NPS-400 dcmac instruction

gas/ChangeLog:

       * testsuite/gas/arc/nps-400-9.d: Added.
       * testsuite/gas/arc/nps-400-9.s: Added.

include/ChangeLog:

       * opcode/arc.h: Add PROTOCOL_DECODE to insn_class_t.

opcodes/ChangeLog:

       * arc-dis.c (arc_insn_length): Return length 8 for instructions with
       major opcode 0xa.
       * arc-nps-400-tbl.h: Add dcmac instruction.
       * arc-opc.c (arc_operands): Added operands for dcmac instruction.
       (insert_nps_rbdouble_64): Added.
       (extract_nps_rbdouble_64): Added.
       (insert_nps_proto_size): Added.
       (extract_nps_proto_size): Added.