S12Z: opcodes: Separate the decoding of operations from their display.

S12Z: opcodes: Separate the decoding of operations from their display.

This change adds an abstraction layer between the decoding of machine
operations and their disassembled textual representation.  This allows
the decoding routines to be re-used for other purposes (at the expense)
of slightly slower running time.

ChangeLog: opcodes/

   * s12z-opc.c: New file.
   * s12z-opc.h: New file.
   * s12z-dis.c: Removed all code not directly related to display
     of instructions.  Used the interface provided by the new files
     instead.
   * Makefile.am (TARGET_LIBOPCODES_CFILES) Add s12z-opc.c.
   * Makefile.in: regenerate.
   * configure.ac (bfd_s12z_arch): Correct the dependencies.
   * configure: regenerate.