Renaming .debug to .zdebug and vice versa

Move a couple of elf.c functions to compress.c.

	* compress.c (bfd_debug_name_to_zdebug): New inline function.
	(bfd_zdebug_name_to_debug): Likewise.
	* elf.c (convert_debug_to_zdebug, convert_zdebug_to_debug): Delete.
	(_bfd_elf_make_section_from_shdr, elf_fake_sections),
	(_bfd_elf_assign_file_positions_for_non_load): Adjust to suit.
	* coffgen.c (make_a_section_from_file): Use new inlines here.