[ARC] Fix support for double assist instructions.

[ARC] Fix support for double assist instructions.

opcodes/
2016-04-05  Claudiu Zissulescu  <claziss@synopsys.com>

        * arc-regs.h: Add a new subclass field.  Add double assist
        accumulator register values.
        * arc-tbl.h: Use DPA subclass to mark the double assist
        instructions.  Use DPX/SPX subclas to mark the FPX instructions.
        * arc-opc.c (RSP): Define instead of SP.
        (arc_aux_regs): Add the subclass field.

include/
2016-04-05  Claudiu Zissulescu  <claziss@synopsys.com>

        * opcode/arc.h (DPA, DPX, SPX): New subclass enums.
        (ARC_FPUDA): Define.
        (arc_aux_reg): Add new field.

gas/
2016-04-05  Claudiu Zissulescu  <claziss@synopsys.com>

        * config/tc-arc.c (is_code_density_p): Compare directly the
        subclass field.
        (is_spfp_p, is_dpfp_p, is_spfp_p): Define.
        (check_cpu_feature): New function.
        (find_opcode_match): Use check_cpu_feature function.
        (preprocess_operands): Likewise.
        (md_parse_option): Use mfpuda, mdpfp, mspfp options.
        * testsuite/gas/arc/tdpfp.d: New file.
        * testsuite/gas/arc/tfpuda.d: Likewise.
        * testsuite/gas/arc/tfpx.s: Likewise.