x86: Add _bfd_x86_elf_finish_dynamic_sections

x86: Add _bfd_x86_elf_finish_dynamic_sections

Extract the common parts of elf_i386_finish_dynamic_sections and
elf_x86_64_finish_dynamic_sections into a separate function in
elfxx-x86.c.

	* elf32-i386.c (elf_i386_finish_dynamic_sections): Call
	_bfd_x86_elf_finish_dynamic_sections.
	* elf64-x86-64.c (elf_x86_64_finish_dynamic_sections): Likewise.
	* elfxx-x86.c (_bfd_x86_elf_finish_dynamic_sections): New
	function.
	* elfxx-x86.h (_bfd_x86_elf_finish_dynamic_sections): New
	prototype.