objdump: add DWARF support for AIX

objdump: add DWARF support for AIX

DWARF sections have special names on AIX which need be handled
by objdump in order to correctly print them.
This patch also adds the correlation in bfd for future uses.

bfd/
	* libxcoff.h (struct xcoff_dwsect_name): Add DWARF name.
	* coff-rs6000.c (xcoff_dwsect_names): Update.
	* coffcode.h (sec_to_styp_flags): Likewise.
	(coff_new_section_hook): Likewise.
binutils/
	* dwarf.h (struct dwarf_section): Add XCOFF name.
	* dwarf.c (struct dwarf_section_display): Update.
	* objdump.c (load_debug_section): Add XCOFF name handler.
	(dump_dwarf_section): Likewise.
gas/
	* config/tc-ppc.c (ppc_change_debug_section): Update to
	match new name's field.