csky: fix annobin test fails

	* elf32-csky.c (is_mapping_symbol_name): New function.
	(csky_elf_is_target_special_symbol): Likewise.
	(csky_elf_maybe_function_sym): Likewise.
	(bfd_elf32_bfd_is_target_special_symbol): Define.
	(elf_backend_maybe_function_sym): Define.