Use bfd_malloc_and_get_section

Use bfd_malloc_and_get_section

It's nicer than xmalloc followed by bfd_get_section_contents, since
xmalloc exits on failure and needs a check that its size_t arg doesn't
lose high bits when converted from bfd_size_type.

	PR binutils/21665
	* objdump.c (strtab): Make var a bfd_byte*.
	(disassemble_section): Don't limit malloc size.  Instead, use
	bfd_malloc_and_get_section.
	(read_section_stabs): Use bfd_malloc_and_get_section.  Return
	bfd_byte*.
	(find_stabs_section): Remove now unnecessary cast.
	* objcopy.c (copy_object): Use bfd_malloc_and_get_section.  Free
	contents on error return.
	* nlmconv.c (copy_sections): Use bfd_malloc_and_get_section.