[ARC] Update disassembler opcode selection

[ARC] Update disassembler opcode selection

New instruction are added, and some of them are overlapping. Update
disassembler to correctly recognize them. Introduce nps400 option.

opcodes/
xxxx-xx-xx  Claudiu Zissulescu  <claziss@synopsys.com>

	* arc-dis.c (skip_this_opcode): Check also for 0x07 major opcodes,
	and MPY class instructions.
	(parse_option): Add nps400 option.
	(print_arc_disassembler_options): Add nps400 info.

gas/
xxxx-xx-xx  Claudiu Zissulescu  <claziss@synopsys.com>

	* testsuite/gas/arc/nps400-6.d: Update test.