nios2: Add disas entries

Add nios2 disassembler support. This patch is composed from binutils files
from commit "Opcodes and assembler support for Nios II R2". The files from
binutils used in this patch are:

    include/opcode/nios2.h
    include/opcode/nios2r1.h
    include/opcode/nios2r2.h
    opcodes/nios2-opc.c
    opcodes/nios2-dis.c

Checkpatch says total: 114 errors, 0 warnings, 3609 lines checked , which
is caused by a different coding style in those files. These warnings and
errors are not addressed To let these files be easily synchronized between
binutils and qemu.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chris Wulff <crwulff@gmail.com>
Cc: Jeff Da Silva <jdasilva@altera.com>
Cc: Ley Foon Tan <lftan@altera.com>
Cc: Sandra Loosemore <sandra@codesourcery.com>
Cc: Yves Vandervennet <yvanderv@altera.com>
Reviewed-by: Alexander Graf <agraf@suse.de>
Message-Id: <20170118220146.489-2-marex@denx.de>
Signed-off-by: Richard Henderson <rth@twiddle.net>
