arc: Add disassembler helper

arc: Add disassembler helper

Add disassembler helper for GDB, that uses opcodes structure arc_instruction
and adds convenience functions to handle instruction operands.  This interface
solves at least those problems with arc_instruction:

  * Some instructions, like "push_s", have implicit operands which are not
    directly present in arc_instruction.
  * Operands of particular meaning, like branch/jump targets, have various
    locations and meaning depending on type of branch/target.
  * Access to operand value is abstracted into a separate function, so callee
    code shouldn't bother if operand value is an immediate value or in a
    register.

Testcases included in this commit are fairly limited - they test exclusively
branch instructions, something that will be used in software single stepping.
Most of the other parts of this disassembler helper are tested during prologue
analysis testing.

gdb/ChangeLog:

yyyy-mm-dd  Anton Kolesov  <anton.kolesov@synopsys.com>

	* configure.tgt: Add arc-insn.o.
	* arc-tdep.c (arc_delayed_print_insn): Make non-static.
	(dump_arc_instruction_command): New function.
	(arc_fprintf_disasm): Likewise.
	(arc_disassemble_info): Likewise.
	(arc_insn_get_operand_value): Likewise.
	(arc_insn_get_operand_value_signed): Likewise.
	(arc_insn_get_memory_base_reg): Likewise.
	(arc_insn_get_memory_offset): Likewise.
	(arc_insn_get_branch_target): Likewise.
	(arc_insn_dump): Likewise.
	(arc_insn_get_linear_next_pc): Likewise.
	* arc-tdep.h (arc_delayed_print_insn): Add function declaration.
	(arc_disassemble_info): Likewise.
	(arc_insn_get_branch_target): Likewise.
	(arc_insn_get_linear_next_pc): Likewise.
	* NEWS: Mention new "maint print arc arc-instruction".

gdb/doc/ChangeLog:

yyyy-mm-dd  Anton Kolesov  <anton.kolesov@synopsys.com>

	* gdb.texinfo (Synopsys ARC): Add "maint print arc arc-instruction".

gdb/testsuite/ChangeLog:

yyyy-mm-dd  Anton Kolesov  <anton.kolesov@synopsys.com>

	* gdb.arch/arc-decode-insn.S: New file.
	* gdb.arch/arc-decode-insn.exp: Likewise.